UCKL1 is a 548-amino-acid uridine-kinase-family enzyme that phosphorylates uridine and cytidine with ATP to generate UMP and CMP, respectively, thereby supporting pyrimidine nucleoside salvage. The protein is predominantly cytoplasmic under basal conditions, while the full-length form can accumulate in the nucleus after binding Epstein-Barr virus EBNA3. RNF19B/NKLAM binds, ubiquitinates, and promotes degradation of UCKL1. UCKL1 abundance influences proliferation, apoptosis, and susceptibility to natural-killer-cell-mediated killing in tumor models. A recent study also reports a kinase-independent, nuclear UCK2-UCKL1 scaffold that promotes TGF-beta/SMAD3-dependent cardiac fibroblast activation after myocardial infarction. The C-terminal half is structurally UPRT-like, but uracil phosphoribosyltransferase activity has not been demonstrated.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0004849
uridine kinase activity
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: The IBA assignment matches direct biochemical evidence that purified human UCKL1 phosphorylates uridine with ATP.
Reason: Uridine kinase activity is one of UCKL1's two directly demonstrated core molecular activities and is phylogenetically consistent with its uridine-kinase-family membership.
Supporting Evidence:
PMID:35583288
Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
|
|
GO:0005737
cytoplasm
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Cytoplasm is the best-supported default location: full-length GFP-UCKL1 was cytoplasmic before EBNA3 expression and endogenous protein was cytoplasmic in EBV-negative lymphoma cells.
Reason: This broad location is supported by phylogenetic inference, direct imaging, UniProt curation, and cytosolic Reactome pathway placement. Nuclear localization is conditional and does not invalidate a cytoplasmic pool.
Supporting Evidence:
PMID:12199906
The predominantly cytoplasmic GFP-F538 translocates to the nucleus when EBNA-3 is expressed.
|
|
GO:0004849
uridine kinase activity
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: The automated uridine kinase assignment agrees with the direct 2022 biochemical characterization.
Reason: Although this row duplicates stronger IBA and IDA evidence, it is accurate; independent annotations with different evidence codes are valid.
Supporting Evidence:
PMID:35583288
Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
|
|
GO:0005524
ATP binding
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: UCKL1 contains a predicted ATP-binding P-loop and purified UCKL1 uses ATP as the phosphate donor in its kinase reactions.
Reason: ATP binding is mechanistically integral to the directly demonstrated nucleoside-kinase reaction and the InterPro mapping is consistent with experimental donor usage.
Supporting Evidence:
PMID:35583288
We analyzed the phosphorylation of both uridine and cytidine with ATP as the phosphate donor.
|
|
GO:0005634
nucleus
|
IEA
GO_REF:0000044 |
KEEP AS NON CORE |
Summary: Nuclear UCKL1 is experimentally observed, but the best-established 2002 localization is EBNA3-dependent and differs between full-length and C-terminally truncated forms.
Reason: Retain nucleus as a real contextual location rather than a default core location. Full-length UCKL1 accumulates in the nucleus with EBNA3, while the truncated isoform remains cytoplasmic; a 2025 cardiac-fibroblast study also reports a nuclear UCK2-UCKL1 pool.
Supporting Evidence:
PMID:12199906
The predominantly cytoplasmic GFP-F538 translocates to the nucleus when EBNA-3 is expressed.
PMID:12199906
GFP-F538ÎC is not targeted to the nucleus by EBNA-3.
|
|
GO:0005737
cytoplasm
|
IEA
GO_REF:0000044 |
ACCEPT |
Summary: UniProt subcellular-location mapping accurately captures the predominant basal localization observed for full-length and truncated UCKL1.
Reason: Direct fluorescence and antibody staining support a cytoplasmic pool, and this location is compatible with cytosolic pyrimidine salvage.
Supporting Evidence:
PMID:12199906
The predominantly cytoplasmic GFP-F538 translocates to the nucleus when EBNA-3 is expressed.
|
|
GO:0008655
pyrimidine-containing compound salvage
|
IEA
GO_REF:0000117 |
ACCEPT |
Summary: UCKL1 generates UMP and CMP from pyrimidine nucleosides, placing it directly in pyrimidine-containing compound salvage.
Reason: The ARBA-derived process is broad but biologically central and is supported by direct enzymology plus independent genetic evidence for uridine salvage.
Supporting Evidence:
PMID:35583288
Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
PMID:39592843
We therefore generated a cell line also lacking the predicted UCK, UCKL1 (UCK tKO), and observed that uridine was unable to rescue the effects of de novo pyrimidine synthesis inhibition on proliferation and Chk1 phosphorylation, confirming the absence of UCK activity (Fig. 3c and Extended Data Fig. 4d).
|
|
GO:0009224
CMP biosynthetic process
|
IEA
GO_REF:0000108 |
MODIFY |
Summary: UCKL1 does produce CMP from cytidine, but this broad logical-inference term obscures that the reaction is specifically the first step of CTP salvage.
Reason: Replace the generic CMP biosynthetic-process assignment with the pathway-specific CTP salvage term already supported by the same cytidine-kinase reaction and UniPathway annotation.
Proposed replacements:
CTP salvage
Supporting Evidence:
PMID:35583288
Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
|
|
GO:0016301
kinase activity
|
IEA
GO_REF:0000002 |
MARK AS OVER ANNOTATED |
Summary: UCKL1 is a kinase, but this parent term is much less informative than the directly demonstrated uridine kinase and cytidine kinase activities.
Reason: The InterPro mapping is technically correct but redundant and overly broad now that substrate-specific molecular-function terms are available.
Supporting Evidence:
PMID:35583288
Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
|
|
GO:0043771
cytidine kinase activity
|
IEA
GO_REF:0000116 |
ACCEPT |
Summary: Rhea mapping correctly assigns cytidine kinase activity, which purified UCKL1 directly demonstrates.
Reason: Cytidine kinase activity is a core UCKL1 molecular function; this IEA row agrees with the IDA annotation and the curated Rhea reaction.
Supporting Evidence:
PMID:35583288
Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
|
|
GO:0055086
nucleobase-containing small molecule metabolic process
|
IEA
GO_REF:0000117 |
MARK AS OVER ANNOTATED |
Summary: UCKL1 participates in this very broad metabolic parent through pyrimidine nucleoside salvage, but the term does not identify its actual pathway.
Reason: More specific accepted terms for pyrimidine nucleoside, UMP, and CTP salvage capture the supported biology without the loss of information inherent in this ARBA parent.
Supporting Evidence:
PMID:35583288
Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
|
|
GO:1901137
carbohydrate derivative biosynthetic process
|
IEA
GO_REF:0000117 |
MARK AS OVER ANNOTATED |
Summary: Nucleotide synthesis falls under this extremely broad parent, but the term is not informative about UCKL1's direct salvage reactions.
Reason: The ARBA inference is not false, but UMP and CTP salvage terms describe the supported process at the appropriate specificity.
Supporting Evidence:
PMID:35583288
Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
|
|
GO:0005515
protein binding
|
IPI
PMID:12199906 Epstein-Barr virus encoded nuclear protein EBNA-3 binds a no... |
MARK AS OVER ANNOTATED |
Summary: UCKL1/F538 specifically binds EBV EBNA3, and the interaction drives conditional nuclear relocalization, but bare protein binding is uninformative as a molecular function.
Reason: The interaction is experimentally real and is retained in the review, but GO:0005515 does not communicate the host-virus context or functional consequence and should not be treated as a core UCKL1 activity.
Supporting Evidence:
PMID:12199906
We have shown that F538 interacts specifically with EBNA-3 in the yeast two-hybrid system and in GST pull down assays.
|
|
GO:0005515
protein binding
|
IPI
PMID:16709802 NK lytic-associated molecule, involved in NK cytotoxic funct... |
MODIFY |
Summary: RNF19B/NKLAM binds UCKL1 as an E3-ligase substrate and promotes its ubiquitination and reduced abundance.
Reason: The interaction is explicit in the abstract-only source and is more informatively represented by ubiquitin protein ligase binding than by generic protein binding.
Proposed replacements:
ubiquitin protein ligase binding
Supporting Evidence:
PMID:16709802
We confirmed that NKLAM and URKL-1 interact in mammalian cells by using both immunoprecipitation and confocal microscopy.
PMID:16709802
We demonstrated decreased protein expression and enhanced ubiquitination of URKL-1 in the presence of NKLAM.
|
|
GO:0043097
pyrimidine nucleoside salvage
|
TAS
Reactome:R-HSA-73614 |
ACCEPT |
Summary: Reactome places UCKL1 in pyrimidine nucleoside salvage, consistent with direct uridine and cytidine phosphorylation.
Reason: This is the appropriate shared process for the two core kinase activities and is independently supported by direct biochemical and genetic evidence.
Supporting Evidence:
Reactome:R-HSA-73614
In pyrimidine salvage reactions, nucleosides and free bases generated by DNA and RNA breakdown are converted back to nucleotide monophosphates, allowing them to re-enter the pathways of pyrimidine biosynthesis and interconversion.
|
|
GO:0004849
uridine kinase activity
|
IDA
PMID:35583288 Characterization of uridine-cytidine kinase like-1 nucleosid... |
ACCEPT |
Summary: Purified recombinant UCKL1 directly phosphorylated uridine with ATP and kinetic parameters were measured.
Reason: This is direct biochemical evidence for a core molecular function and is the strongest evidence supporting the uridine-kinase assignments.
Supporting Evidence:
PMID:35583288
Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
|
|
GO:0043771
cytidine kinase activity
|
IDA
PMID:35583288 Characterization of uridine-cytidine kinase like-1 nucleosid... |
ACCEPT |
Summary: Purified recombinant UCKL1 directly phosphorylated cytidine with ATP and kinetic parameters were measured.
Reason: This is direct biochemical evidence for UCKL1's second core molecular function and supports its placement in CTP salvage.
Supporting Evidence:
PMID:35583288
Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
|
|
GO:0044206
UMP salvage
|
IEA
GO_REF:0000041 |
ACCEPT |
Summary: UCKL1 converts uridine to UMP, the defining reaction of UMP salvage.
Reason: The UniPathway mapping is mechanistically supported by direct uridine kinase activity and independent genetic evidence for UCK-dependent uridine rescue.
Supporting Evidence:
PMID:35583288
Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
PMID:39592843
We therefore generated a cell line also lacking the predicted UCK, UCKL1 (UCK tKO), and observed that uridine was unable to rescue the effects of de novo pyrimidine synthesis inhibition on proliferation and Chk1 phosphorylation, confirming the absence of UCK activity (Fig. 3c and Extended Data Fig. 4d).
|
|
GO:0044211
CTP salvage
|
IEA
GO_REF:0000041 |
ACCEPT |
Summary: UCKL1 converts cytidine to CMP, the first step in salvage of cytidine to CTP.
Reason: The UniPathway mapping follows directly from experimentally demonstrated cytidine kinase activity and is the most informative process term for that reaction.
Supporting Evidence:
PMID:35583288
Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
|
|
GO:0004849
uridine kinase activity
|
TAS
Reactome:R-HSA-8954327 |
ACCEPT |
Summary: Reactome's uridine-phosphorylation event predates direct UCKL1 enzymology but is now confirmed by the 2022 biochemical study.
Reason: The event accurately captures a core activity. Its older sequence-based UPRT speculation should not be extended into a UPRT annotation.
Supporting Evidence:
Reactome:R-HSA-8954327
Based on sequence similarity, cytosolic uridine-cytidine kinase-like 1 (UCKL1 aka F538) is thought to function as a novel human uridine kinase/uracil phosphoribosyltransferase (Kashuba et al. 2002).
PMID:35583288
Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
|
|
GO:0005634
nucleus
|
EXP
PMID:12199906 Epstein-Barr virus encoded nuclear protein EBNA-3 binds a no... |
KEEP AS NON CORE |
Summary: Full-length UCKL1/F538 accumulates in the nucleus when EBNA3 is expressed; endogenous protein is also predominantly nuclear in EBV-positive cells.
Reason: Accept the experimental observation while classifying it as a host-virus-dependent, isoform-sensitive location rather than UCKL1's default functional compartment.
Supporting Evidence:
PMID:12199906
The predominantly cytoplasmic GFP-F538 translocates to the nucleus when EBNA-3 is expressed.
PMID:12199906
GFP-F538ÎC is not targeted to the nucleus by EBNA-3.
|
|
GO:0005737
cytoplasm
|
EXP
PMID:12199906 Epstein-Barr virus encoded nuclear protein EBNA-3 binds a no... |
ACCEPT |
Summary: Direct fluorescence and antibody staining show cytoplasmic UCKL1 in the absence of EBNA3.
Reason: This is direct experimental support for UCKL1's predominant basal location and is compatible with its pyrimidine-salvage activity.
Supporting Evidence:
PMID:12199906
The predominantly cytoplasmic GFP-F538 translocates to the nucleus when EBNA-3 is expressed.
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-8954327 |
ACCEPT |
Summary: Reactome models the UCKL1 phosphorylation event in the cytosol, a more specific location compatible with the experimentally observed cytoplasmic pool.
Reason: Retain the TAS location because it is pathway-compatible and nested within the directly supported cytoplasm annotation, while recognizing that nuclear pools occur in specific contexts.
Supporting Evidence:
Reactome:R-HSA-8954327
Based on sequence similarity, cytosolic uridine-cytidine kinase-like 1 (UCKL1 aka F538) is thought to function as a novel human uridine kinase/uracil phosphoribosyltransferase (Kashuba et al. 2002).
|
Q: Does the C-terminal phosphoribosyltransferase-like domain of human UCKL1 catalyze PRPP-dependent uracil phosphoribosyltransferase activity under any physiological condition?
Suggested experts: Elise C. Matchett, Elise C. Ambrose, Jacki Kornbluth, Elena Kashuba
Q: Are the tumor-cell survival, NF-kappaB, and nucleoside-analogue phenotypes caused by UCKL1 kinase activity, by a kinase-independent scaffold function, or by both?
Suggested experts: Elise C. Ambrose, Jacki Kornbluth, Richard G. Hoover
Q: Is the reported kinase-independent nuclear UCK2-UCKL1-TRIM21 scaffold a reproducible endogenous mechanism in human post-infarction cardiac fibroblasts, and which UCKL1 interface is required?
Suggested experts: Xiao Zhou, Yu Zhang, Yongyi Wang
Q: Which UCKL1 splice isoforms retain nucleoside kinase activity, and how do their C-terminal differences control EBNA3-, RNF19B-, or TGF-beta-dependent localization and turnover?
Suggested experts: Elena Kashuba, Jacki Kornbluth
Experiment: Assay full-length UCKL1 and isolated or active-site-mutated C-terminal domains for conversion of uracil plus PRPP to UMP using orthogonal LC-MS-based product detection and appropriate active UPRT controls.
Hypothesis: The UPRT-like C-terminal domain is either catalytically active only under specific cofactor or oligomerization conditions, or is a catalytically inactive structural domain.
Type: Purified-enzyme biochemistry
Experiment: Create UCKL1-null human cells and rescue them at endogenous abundance with wild-type or kinase-dead UCKL1, then quantify labeled uridine and cytidine flux into UMP/CMP/UTP/CTP together with proliferation, apoptosis, NF-kappaB activity, and NK-cell killing.
Hypothesis: Pyrimidine-salvage flux requires UCKL1 kinase activity, whereas some survival or signaling phenotypes persist with catalytically inactive UCKL1.
Type: Catalytic-dead endogenous rescue and isotope tracing
Experiment: Tag individual endogenous UCKL1 isoforms and follow their localization, interaction, ubiquitination, and half-life after EBNA3 expression, RNF19B induction, or TGF-beta activation without overexpression.
Hypothesis: The C-terminal region controls partner-specific nuclear trafficking and degradation independently of the shared N-terminal nucleoside-kinase domain.
Type: Isoform-resolved endogenous localization
Experiment: Reproduce the UCK2-UCKL1-TRIM21-Smurf2/SMAD3 mechanism with orthogonal endogenous proximity labeling, separation-of-function interface mutants, kinase-dead knock-in rescue, and fibroblast-specific loss and rescue in a second myocardial-infarction model.
Hypothesis: UCKL1 has a genuine kinase-independent scaffold activity in activated cardiac fibroblasts that is separable from pyrimidine salvage.
Type: Independent cardiac-fibroblast mechanism replication
just fetch-gene human UCKL1; the GOA snapshot contained 23 annotations.just deep-research-falcon human UCKL1 --fallback perplexity-lite. Falcon failed with HTTP 402 and the automatic Perplexity-lite fallback failed with HTTP 401/quota exhaustion. No provider-named deep-research file was created. The review therefore relies on the reviewed UniProt record, GOA, cached primary publications, Reactome records, and a targeted PubMed/PMC freshness search.just fetch-gene-pmids human UCKL1 successfully cached every PMID cited by GOA. Additional direct UCKL1 papers found during the freshness search were cached and read.Human UCKL1 is a 548-aa uridine-kinase-family protein with an N-terminal P-loop/uridine-kinase-like region and a C-terminal phosphoribosyltransferase-like region. The decisive biochemical evidence is the 2022 study of purified recombinant UCKL1: it reports that "Both enzymes efficiently phosphorylated uridine and cytidine" and that ATP was the phosphate donor PMID:35583288. The same paper measured UCKL1 kinetic parameters for both substrates and concluded that it is a pyrimidine kinase PMID:35583288. This directly supports uridine kinase activity (GO:0004849), cytidine kinase activity (GO:0043771), UMP salvage, CTP salvage, and the broader pyrimidine-nucleoside salvage process.
A 2024 study provides independent genetic support in Jurkat cells. UCK1/UCK2 double-knockout cells retained uridine-rescue activity; deletion of UCKL1 to make a triple knockout eliminated uridine rescue of de novo pyrimidine-synthesis inhibition PMID:39592843. Because this is a triple-knockout comparison rather than an isolated UCKL1 rescue, it corroborates but does not by itself quantify UCKL1-specific flux.
The C-terminal region was originally modeled as UPRT-like, but the 2002 paper's dual UK/UPRT assignment was a sequence/structure-based proposal, not a direct enzymatic measurement PMID:12199906. The 2022 investigators explicitly stated that UPRT activity was still under examination PMID:35583288. No UPRT molecular-function annotation is therefore warranted from the available evidence.
Reactome places UCKL1 in cytosolic pyrimidine salvage and describes uridine/cytidine phosphorylation, although its event text predates the direct 2022 biochemical demonstration and was initially based on sequence similarity [Reactome:R-HSA-8954327 "Based on sequence similarity, cytosolic uridine-cytidine kinase-like 1 (UCKL1 aka F538) is thought to function as a novel human uridine kinase/uracil phosphoribosyltransferase (Kashuba et al. 2002)."].
The full-length protein was predominantly cytoplasmic when expressed in CV-1 cells, and endogenous UCKL1/F538 staining was almost exclusively cytoplasmic in EBV-negative Burkitt lymphoma cells PMID:12199906. EBV EBNA3 binds UCKL1 and induces nuclear accumulation of the full-length form; the C-terminally truncated isoform 3 remains cytoplasmic PMID:12199906. Thus cytoplasm/cytosol is the best-supported default functional location, whereas nucleus is a real but condition- and isoform-sensitive non-core location.
UniProt lists four splice isoforms. Isoform 3 terminates after residue 395 and lacks most of the C-terminal phosphoribosyltransferase-like region. The 2002 study did not directly measure isoform-specific kinase activity, so the fact that this isoform retains the N-terminal kinase-like domain should be treated as a hypothesis rather than a demonstrated functional distinction.
UCKL1 directly interacts with EBV EBNA3 in yeast two-hybrid and GST pull-down assays PMID:12199906. The generic GO molecular-function term protein binding does not communicate the biological meaning of this host-virus interaction, so the corresponding annotation is retained only as an over-annotated interaction record.
RNF19B/NKLAM is an E3 ubiquitin ligase that binds UCKL1, ubiquitinates it, and lowers its abundance. The abstract-only 2006 paper explicitly reports mammalian-cell interaction and enhanced UCKL1 ubiquitination PMID:16709802 PMID:16709802. The RNF19B-derived generic protein-binding row can therefore be made more informative as ubiquitin protein ligase binding (GO:0031625). Full text is not available in the local cache, but the required interaction and substrate claims are explicit in the abstract.
UCKL1 dosage affects proliferation and apoptosis in tumor-cell models. RNAi in K562 erythroleukemia cells initiated apoptosis, slowed the cell cycle, reduced growth, and increased susceptibility to drug- and NK-mediated killing PMID:19653100. Conversely, overexpression protected tumor cells from NK-mediated and drug-induced apoptosis and increased proliferation PMID:32083188. UCKL1 expression also contributed to the cytotoxic action of the uridine analogue EUrd in temozolomide-resistant glioblastoma-initiating cells PMID:27090194. These are strong disease-model phenotypes, but the available work does not establish whether they are caused by uridine/cytidine kinase activity, another domain, or both; they should not be converted directly into broad normal-process GO annotations.
A 2025 study reports a distinct, context-specific role in TGF-ÎČ-activated human cardiac fibroblasts and post-infarction mouse hearts. Endogenous UCK2 and UCKL1 co-immunoprecipitated and colocalized predominantly in the nucleus PMID:41457201. UCKL1 knockdown attenuated fibroblast differentiation, proliferation, and migration; the study proposes that a UCK2/UCKL1 complex recruits TRIM21 to regulate Smurf2/Smad3 signaling PMID:41457201. Kinase-dead proteins retained the profibrotic phenotype PMID:41457201. This recent single-study scaffold model is biologically important but is not treated as a second core evolved function until independently replicated and more precisely mapped.
protein binding with EBNA3 is uninformative and marked over-annotated; generic binding with RNF19B is modified to ubiquitin protein ligase binding.kinase activity, nucleobase-containing small molecule metabolic process, and carbohydrate derivative biosynthetic process) are technically compatible but over-annotated relative to the direct specific terms.CMP biosynthetic process is modified to the more pathway-specific CTP salvage term.id: Q9NWZ5
gene_symbol: UCKL1
product_type: PROTEIN
status: COMPLETE
taxon:
id: NCBITaxon:9606
label: Homo sapiens
description: >-
UCKL1 is a 548-amino-acid uridine-kinase-family enzyme that phosphorylates
uridine and cytidine with ATP to generate UMP and CMP, respectively, thereby
supporting pyrimidine nucleoside salvage. The protein is predominantly
cytoplasmic under basal conditions, while the full-length form can accumulate
in the nucleus after binding Epstein-Barr virus EBNA3. RNF19B/NKLAM binds,
ubiquitinates, and promotes degradation of UCKL1. UCKL1 abundance influences
proliferation, apoptosis, and susceptibility to natural-killer-cell-mediated
killing in tumor models. A recent study also reports a kinase-independent,
nuclear UCK2-UCKL1 scaffold that promotes TGF-beta/SMAD3-dependent cardiac
fibroblast activation after myocardial infarction. The C-terminal half is
structurally UPRT-like, but uracil phosphoribosyltransferase activity has not
been demonstrated.
alternative_products:
- name: '1'
id: Q9NWZ5-1
description: Full-length canonical isoform used for the direct kinase assays
and capable of EBNA3-dependent nuclear relocalization.
- name: '2'
id: Q9NWZ5-2
sequence_note: VSP_021802
description: Alternative C-terminal sequence after residue 302; no
isoform-specific biochemical function has been established.
- name: '3'
id: Q9NWZ5-3
sequence_note: VSP_025641, VSP_025642
description: C-terminally truncated after residue 395; remains cytoplasmic in
the presence of EBNA3, unlike the full-length form.
- name: '4'
id: Q9NWZ5-4
sequence_note: VSP_043171
description: Alternative N-terminal sequence; no isoform-specific biochemical
function has been established.
existing_annotations:
- term:
id: GO:0004849
label: uridine kinase activity
evidence_type: IBA
original_reference_id: GO_REF:0000033
qualifier: enables
review:
summary: >-
The IBA assignment matches direct biochemical evidence that purified human
UCKL1 phosphorylates uridine with ATP.
action: ACCEPT
reason: >-
Uridine kinase activity is one of UCKL1's two directly demonstrated core
molecular activities and is phylogenetically consistent with its
uridine-kinase-family membership.
supported_by:
- reference_id: PMID:35583288
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
- term:
id: GO:0005737
label: cytoplasm
evidence_type: IBA
original_reference_id: GO_REF:0000033
qualifier: is_active_in
review:
summary: >-
Cytoplasm is the best-supported default location: full-length GFP-UCKL1
was cytoplasmic before EBNA3 expression and endogenous protein was
cytoplasmic in EBV-negative lymphoma cells.
action: ACCEPT
reason: >-
This broad location is supported by phylogenetic inference, direct imaging,
UniProt curation, and cytosolic Reactome pathway placement. Nuclear
localization is conditional and does not invalidate a cytoplasmic pool.
supported_by:
- reference_id: PMID:12199906
supporting_text: The predominantly cytoplasmic GFP-F538 translocates to the nucleus when EBNA-3 is expressed.
reference_section_type: DISCUSSION
- term:
id: GO:0004849
label: uridine kinase activity
evidence_type: IEA
original_reference_id: GO_REF:0000120
qualifier: enables
review:
summary: >-
The automated uridine kinase assignment agrees with the direct 2022
biochemical characterization.
action: ACCEPT
reason: >-
Although this row duplicates stronger IBA and IDA evidence, it is accurate;
independent annotations with different evidence codes are valid.
supported_by:
- reference_id: PMID:35583288
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
- term:
id: GO:0005524
label: ATP binding
evidence_type: IEA
original_reference_id: GO_REF:0000002
qualifier: enables
review:
summary: >-
UCKL1 contains a predicted ATP-binding P-loop and purified UCKL1 uses ATP
as the phosphate donor in its kinase reactions.
action: ACCEPT
reason: >-
ATP binding is mechanistically integral to the directly demonstrated
nucleoside-kinase reaction and the InterPro mapping is consistent with
experimental donor usage.
supported_by:
- reference_id: PMID:35583288
supporting_text: We analyzed the phosphorylation of both uridine and cytidine with ATP as the phosphate donor.
reference_section_type: DISCUSSION
- term:
id: GO:0005634
label: nucleus
evidence_type: IEA
original_reference_id: GO_REF:0000044
qualifier: located_in
review:
summary: >-
Nuclear UCKL1 is experimentally observed, but the best-established 2002
localization is EBNA3-dependent and differs between full-length and
C-terminally truncated forms.
action: KEEP_AS_NON_CORE
reason: >-
Retain nucleus as a real contextual location rather than a default core
location. Full-length UCKL1 accumulates in the nucleus with EBNA3, while
the truncated isoform remains cytoplasmic; a 2025 cardiac-fibroblast study
also reports a nuclear UCK2-UCKL1 pool.
supported_by:
- reference_id: PMID:12199906
supporting_text: The predominantly cytoplasmic GFP-F538 translocates to the nucleus when EBNA-3 is expressed.
reference_section_type: DISCUSSION
- reference_id: PMID:12199906
supporting_text: GFP-F538ÎC is not targeted to the nucleus by EBNA-3.
reference_section_type: DISCUSSION
- term:
id: GO:0005737
label: cytoplasm
evidence_type: IEA
original_reference_id: GO_REF:0000044
qualifier: located_in
review:
summary: >-
UniProt subcellular-location mapping accurately captures the predominant
basal localization observed for full-length and truncated UCKL1.
action: ACCEPT
reason: >-
Direct fluorescence and antibody staining support a cytoplasmic pool, and
this location is compatible with cytosolic pyrimidine salvage.
supported_by:
- reference_id: PMID:12199906
supporting_text: The predominantly cytoplasmic GFP-F538 translocates to the nucleus when EBNA-3 is expressed.
reference_section_type: DISCUSSION
- term:
id: GO:0008655
label: pyrimidine-containing compound salvage
evidence_type: IEA
original_reference_id: GO_REF:0000117
qualifier: involved_in
review:
summary: >-
UCKL1 generates UMP and CMP from pyrimidine nucleosides, placing it
directly in pyrimidine-containing compound salvage.
action: ACCEPT
reason: >-
The ARBA-derived process is broad but biologically central and is supported
by direct enzymology plus independent genetic evidence for uridine salvage.
supported_by:
- reference_id: PMID:35583288
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
- reference_id: PMID:39592843
supporting_text: >-
We therefore generated a cell line also lacking the predicted UCK, UCKL1
(UCK tKO), and observed that uridine was unable to rescue the effects of
de novo pyrimidine synthesis inhibition on proliferation and Chk1
phosphorylation, confirming the absence of UCK activity (Fig. 3c and
Extended Data Fig. 4d).
reference_section_type: RESULTS
- term:
id: GO:0009224
label: CMP biosynthetic process
evidence_type: IEA
original_reference_id: GO_REF:0000108
qualifier: involved_in
review:
summary: >-
UCKL1 does produce CMP from cytidine, but this broad logical-inference term
obscures that the reaction is specifically the first step of CTP salvage.
action: MODIFY
reason: >-
Replace the generic CMP biosynthetic-process assignment with the
pathway-specific CTP salvage term already supported by the same
cytidine-kinase reaction and UniPathway annotation.
proposed_replacement_terms:
- id: GO:0044211
label: CTP salvage
supported_by:
- reference_id: PMID:35583288
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
- term:
id: GO:0016301
label: kinase activity
evidence_type: IEA
original_reference_id: GO_REF:0000002
qualifier: enables
review:
summary: >-
UCKL1 is a kinase, but this parent term is much less informative than the
directly demonstrated uridine kinase and cytidine kinase activities.
action: MARK_AS_OVER_ANNOTATED
reason: >-
The InterPro mapping is technically correct but redundant and overly broad
now that substrate-specific molecular-function terms are available.
supported_by:
- reference_id: PMID:35583288
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
- term:
id: GO:0043771
label: cytidine kinase activity
evidence_type: IEA
original_reference_id: GO_REF:0000116
qualifier: enables
review:
summary: >-
Rhea mapping correctly assigns cytidine kinase activity, which purified
UCKL1 directly demonstrates.
action: ACCEPT
reason: >-
Cytidine kinase activity is a core UCKL1 molecular function; this IEA row
agrees with the IDA annotation and the curated Rhea reaction.
supported_by:
- reference_id: PMID:35583288
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
- term:
id: GO:0055086
label: nucleobase-containing small molecule metabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000117
qualifier: involved_in
review:
summary: >-
UCKL1 participates in this very broad metabolic parent through pyrimidine
nucleoside salvage, but the term does not identify its actual pathway.
action: MARK_AS_OVER_ANNOTATED
reason: >-
More specific accepted terms for pyrimidine nucleoside, UMP, and CTP
salvage capture the supported biology without the loss of information
inherent in this ARBA parent.
supported_by:
- reference_id: PMID:35583288
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
- term:
id: GO:1901137
label: carbohydrate derivative biosynthetic process
evidence_type: IEA
original_reference_id: GO_REF:0000117
qualifier: involved_in
review:
summary: >-
Nucleotide synthesis falls under this extremely broad parent, but the term
is not informative about UCKL1's direct salvage reactions.
action: MARK_AS_OVER_ANNOTATED
reason: >-
The ARBA inference is not false, but UMP and CTP salvage terms describe the
supported process at the appropriate specificity.
supported_by:
- reference_id: PMID:35583288
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:12199906
qualifier: enables
review:
summary: >-
UCKL1/F538 specifically binds EBV EBNA3, and the interaction drives
conditional nuclear relocalization, but bare protein binding is
uninformative as a molecular function.
action: MARK_AS_OVER_ANNOTATED
reason: >-
The interaction is experimentally real and is retained in the review, but
GO:0005515 does not communicate the host-virus context or functional
consequence and should not be treated as a core UCKL1 activity.
supported_by:
- reference_id: PMID:12199906
supporting_text: We have shown that F538 interacts specifically with EBNA-3 in the yeast two-hybrid system and in GST pull down assays.
reference_section_type: DISCUSSION
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:16709802
qualifier: enables
review:
summary: >-
RNF19B/NKLAM binds UCKL1 as an E3-ligase substrate and promotes its
ubiquitination and reduced abundance.
action: MODIFY
reason: >-
The interaction is explicit in the abstract-only source and is more
informatively represented by ubiquitin protein ligase binding than by
generic protein binding.
proposed_replacement_terms:
- id: GO:0031625
label: ubiquitin protein ligase binding
supported_by:
- reference_id: PMID:16709802
supporting_text: We confirmed that NKLAM and URKL-1 interact in mammalian cells by using both immunoprecipitation and confocal microscopy.
reference_section_type: ABSTRACT
full_text_unavailable: true
- reference_id: PMID:16709802
supporting_text: We demonstrated decreased protein expression and enhanced ubiquitination of URKL-1 in the presence of NKLAM.
reference_section_type: ABSTRACT
full_text_unavailable: true
- term:
id: GO:0043097
label: pyrimidine nucleoside salvage
evidence_type: TAS
original_reference_id: Reactome:R-HSA-73614
qualifier: involved_in
review:
summary: >-
Reactome places UCKL1 in pyrimidine nucleoside salvage, consistent with
direct uridine and cytidine phosphorylation.
action: ACCEPT
reason: >-
This is the appropriate shared process for the two core kinase activities
and is independently supported by direct biochemical and genetic evidence.
supported_by:
- reference_id: Reactome:R-HSA-73614
supporting_text: >-
In pyrimidine salvage reactions, nucleosides and free bases generated by
DNA and RNA breakdown are converted back to nucleotide monophosphates,
allowing them to re-enter the pathways of pyrimidine biosynthesis and
interconversion.
- term:
id: GO:0004849
label: uridine kinase activity
evidence_type: IDA
original_reference_id: PMID:35583288
qualifier: enables
review:
summary: >-
Purified recombinant UCKL1 directly phosphorylated uridine with ATP and
kinetic parameters were measured.
action: ACCEPT
reason: >-
This is direct biochemical evidence for a core molecular function and is
the strongest evidence supporting the uridine-kinase assignments.
supported_by:
- reference_id: PMID:35583288
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
- term:
id: GO:0043771
label: cytidine kinase activity
evidence_type: IDA
original_reference_id: PMID:35583288
qualifier: enables
review:
summary: >-
Purified recombinant UCKL1 directly phosphorylated cytidine with ATP and
kinetic parameters were measured.
action: ACCEPT
reason: >-
This is direct biochemical evidence for UCKL1's second core molecular
function and supports its placement in CTP salvage.
supported_by:
- reference_id: PMID:35583288
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
- term:
id: GO:0044206
label: UMP salvage
evidence_type: IEA
original_reference_id: GO_REF:0000041
qualifier: involved_in
review:
summary: >-
UCKL1 converts uridine to UMP, the defining reaction of UMP salvage.
action: ACCEPT
reason: >-
The UniPathway mapping is mechanistically supported by direct uridine
kinase activity and independent genetic evidence for UCK-dependent uridine
rescue.
supported_by:
- reference_id: PMID:35583288
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
- reference_id: PMID:39592843
supporting_text: >-
We therefore generated a cell line also lacking the predicted UCK, UCKL1
(UCK tKO), and observed that uridine was unable to rescue the effects of
de novo pyrimidine synthesis inhibition on proliferation and Chk1
phosphorylation, confirming the absence of UCK activity (Fig. 3c and
Extended Data Fig. 4d).
reference_section_type: RESULTS
- term:
id: GO:0044211
label: CTP salvage
evidence_type: IEA
original_reference_id: GO_REF:0000041
qualifier: involved_in
review:
summary: >-
UCKL1 converts cytidine to CMP, the first step in salvage of cytidine to
CTP.
action: ACCEPT
reason: >-
The UniPathway mapping follows directly from experimentally demonstrated
cytidine kinase activity and is the most informative process term for that
reaction.
supported_by:
- reference_id: PMID:35583288
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
- term:
id: GO:0004849
label: uridine kinase activity
evidence_type: TAS
original_reference_id: Reactome:R-HSA-8954327
qualifier: enables
review:
summary: >-
Reactome's uridine-phosphorylation event predates direct UCKL1 enzymology
but is now confirmed by the 2022 biochemical study.
action: ACCEPT
reason: >-
The event accurately captures a core activity. Its older sequence-based
UPRT speculation should not be extended into a UPRT annotation.
supported_by:
- reference_id: Reactome:R-HSA-8954327
supporting_text: >-
Based on sequence similarity, cytosolic uridine-cytidine kinase-like 1
(UCKL1 aka F538) is thought to function as a novel human uridine
kinase/uracil phosphoribosyltransferase (Kashuba et al. 2002).
- reference_id: PMID:35583288
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
- term:
id: GO:0005634
label: nucleus
evidence_type: EXP
original_reference_id: PMID:12199906
qualifier: located_in
review:
summary: >-
Full-length UCKL1/F538 accumulates in the nucleus when EBNA3 is expressed;
endogenous protein is also predominantly nuclear in EBV-positive cells.
action: KEEP_AS_NON_CORE
reason: >-
Accept the experimental observation while classifying it as a
host-virus-dependent, isoform-sensitive location rather than UCKL1's
default functional compartment.
supported_by:
- reference_id: PMID:12199906
supporting_text: The predominantly cytoplasmic GFP-F538 translocates to the nucleus when EBNA-3 is expressed.
reference_section_type: DISCUSSION
- reference_id: PMID:12199906
supporting_text: GFP-F538ÎC is not targeted to the nucleus by EBNA-3.
reference_section_type: DISCUSSION
- term:
id: GO:0005737
label: cytoplasm
evidence_type: EXP
original_reference_id: PMID:12199906
qualifier: located_in
review:
summary: >-
Direct fluorescence and antibody staining show cytoplasmic UCKL1 in the
absence of EBNA3.
action: ACCEPT
reason: >-
This is direct experimental support for UCKL1's predominant basal
location and is compatible with its pyrimidine-salvage activity.
supported_by:
- reference_id: PMID:12199906
supporting_text: The predominantly cytoplasmic GFP-F538 translocates to the nucleus when EBNA-3 is expressed.
reference_section_type: DISCUSSION
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-8954327
qualifier: located_in
review:
summary: >-
Reactome models the UCKL1 phosphorylation event in the cytosol, a more
specific location compatible with the experimentally observed
cytoplasmic pool.
action: ACCEPT
reason: >-
Retain the TAS location because it is pathway-compatible and nested within
the directly supported cytoplasm annotation, while recognizing that
nuclear pools occur in specific contexts.
supported_by:
- reference_id: Reactome:R-HSA-8954327
supporting_text: >-
Based on sequence similarity, cytosolic uridine-cytidine kinase-like 1
(UCKL1 aka F538) is thought to function as a novel human uridine
kinase/uracil phosphoribosyltransferase (Kashuba et al. 2002).
references:
- id: GO_REF:0000002
title: Gene Ontology annotation through association of InterPro records with GO terms
findings: []
reference_review:
relevance: MEDIUM
correctness: VERIFIED
review_notes: >-
The UCKL1 GOA row explicitly cites this GO_REF for ATP binding and kinase
activity inferred from InterPro:IPR006083; both mappings were checked
against direct donor usage and the specific kinase annotations.
- id: GO_REF:0000033
title: Annotation inferences using phylogenetic trees
findings: []
reference_review:
relevance: MEDIUM
correctness: VERIFIED
review_notes: >-
The two UCKL1 IBA rows explicitly cite this GO_REF and a PANTHER ancestral
node; the inferred uridine kinase activity and cytoplasm location agree
with direct evidence.
- id: GO_REF:0000041
title: Gene Ontology annotation based on UniPathway vocabulary mapping
findings: []
reference_review:
relevance: MEDIUM
correctness: VERIFIED
review_notes: >-
The GOA rows explicitly map UniPathway UMP and CTP salvage entries to
UCKL1; both pathway assignments are consistent with direct enzymology.
- id: GO_REF:0000044
title: >-
Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
vocabulary mapping, accompanied by conservative changes to GO terms applied
by UniProt
findings: []
reference_review:
relevance: MEDIUM
correctness: VERIFIED
review_notes: >-
The GOA nucleus and cytoplasm rows explicitly cite this UniProt
subcellular-location mapping; the underlying locations were checked
against PMID:12199906.
- id: GO_REF:0000108
title: Automatic assignment of GO terms using logical inference, based on on inter-ontology links
findings: []
reference_review:
relevance: LOW
correctness: VERIFIED
review_notes: >-
The GOA CMP-biosynthetic-process row explicitly cites this inference
method. The inference is mechanistically compatible but less informative
than the pathway-specific CTP salvage term.
- id: GO_REF:0000116
title: Automatic Gene Ontology annotation based on Rhea mapping
findings: []
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
The GOA row explicitly maps RHEA:24674 to cytidine kinase activity; the
same reaction is directly demonstrated in PMID:35583288 and curated in
UniProt.
- id: GO_REF:0000117
title: Electronic Gene Ontology annotations created by ARBA machine learning models
findings: []
reference_review:
relevance: LOW
correctness: VERIFIED
review_notes: >-
The three ARBA-derived GOA rows were checked individually. Pyrimidine
salvage is retained, while the two generic metabolic parents are
classified as over-annotated.
- id: GO_REF:0000120
title: Combined Automated Annotation using Multiple IEA Methods
findings: []
reference_review:
relevance: MEDIUM
correctness: VERIFIED
review_notes: >-
The UCKL1 uridine-kinase IEA row explicitly cites this combined method and
agrees with direct biochemical evidence.
- id: PMID:12199906
title: Epstein-Barr virus encoded nuclear protein EBNA-3 binds a novel human uridine kinase/uracil phosphoribosyltransferase.
findings:
- statement: UCKL1/F538 specifically binds EBV EBNA3.
supporting_text: We have shown that F538 interacts specifically with EBNA-3 in the yeast two-hybrid system and in GST pull down assays.
reference_section_type: DISCUSSION
- statement: Full-length UCKL1 is predominantly cytoplasmic and relocalizes to the nucleus with EBNA3.
supporting_text: The predominantly cytoplasmic GFP-F538 translocates to the nucleus when EBNA-3 is expressed.
reference_section_type: DISCUSSION
- statement: The C-terminally truncated isoform does not undergo EBNA3-dependent nuclear targeting.
supporting_text: GFP-F538ÎC is not targeted to the nucleus by EBNA-3.
reference_section_type: DISCUSSION
- statement: UPRT activity was proposed from sequence and structural modeling rather than measured.
supporting_text: >-
On the basis of the high homology to UK and UK/UPRT and the similar 3D
structure of the C-terminal part of F538 to the T. gondii UPRT, we propose
that F538 is a novel uridine kinas/uracil phosphoribosyltransferase
(UK/UPRT) â an enzyme with double catalytic activity.
reference_section_type: DISCUSSION
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
PMID, title, and full text were checked. The interaction and localization
experiments directly support their uses. The dual UK/UPRT conclusion is
explicitly a modeling-based proposal; later direct work confirms kinase
activity but leaves UPRT activity untested.
- id: PMID:16709802
title: NK lytic-associated molecule, involved in NK cytotoxic function, is an E3 ligase.
full_text_unavailable: true
findings:
- statement: RNF19B/NKLAM and UCKL1 interact in mammalian cells.
supporting_text: We confirmed that NKLAM and URKL-1 interact in mammalian cells by using both immunoprecipitation and confocal microscopy.
reference_section_type: ABSTRACT
full_text_unavailable: true
- statement: RNF19B/NKLAM promotes UCKL1 ubiquitination and lowers its abundance.
supporting_text: We demonstrated decreased protein expression and enhanced ubiquitination of URKL-1 in the presence of NKLAM.
reference_section_type: ABSTRACT
full_text_unavailable: true
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
PMID and title were checked. Only the abstract is cached, but it explicitly
states the mammalian-cell interaction, ubiquitination, and reduced UCKL1
abundance used in this review.
- id: PMID:35583288
title: Characterization of uridine-cytidine kinase like-1 nucleoside kinase activity and its role in tumor growth.
findings:
- statement: Purified UCKL1 phosphorylates uridine and cytidine.
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
- statement: ATP was used as the phosphate donor for both UCKL1 reactions.
supporting_text: We analyzed the phosphorylation of both uridine and cytidine with ATP as the phosphate donor.
reference_section_type: DISCUSSION
- statement: UPRT activity remained under investigation and was not established.
supporting_text: We are also examining whether UCKL-1 has UPRT activity.
reference_section_type: DISCUSSION
- statement: UCKL1 depletion in K562 tumor xenografts increased apoptosis and reduced tumor growth and dissemination.
supporting_text: These results indicate that decreasing UCKL-1 expression in tumor cells induces apoptosis and inhibits tumor growth, dissemination, and metastasis.
reference_section_type: RESULTS
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
PMID, title, and full text were checked. This is the decisive direct
biochemical characterization of both core kinase activities; the
tumor-model experiments are also directly reported.
- id: PMID:19653100
title: Downregulation of uridine-cytidine kinase like-1 decreases proliferation and enhances tumor susceptibility to lysis by apoptotic agents and natural killer cells.
full_text_unavailable: true
findings:
- statement: UCKL1 RNAi in K562 cells induced apoptosis, slowed the cell cycle, and reduced growth.
supporting_text: It was seen that downregulation of UCKL-1 initiated apoptosis and slowed the cell cycle, resulting in lower growth in the small interfering UCKL-1 RNA treated K562 cell culture.
reference_section_type: ABSTRACT
full_text_unavailable: true
reference_review:
relevance: MEDIUM
correctness: VERIFIED
review_notes: >-
PMID and title were checked. Full text is unavailable in the cache, so
only the explicit K562 RNAi phenotype stated in the abstract is used.
- id: PMID:27090194
title: Chemical Screening Identifies EUrd as a Novel Inhibitor Against Temozolomide-Resistant Glioblastoma-Initiating Cells.
full_text_unavailable: true
findings:
- statement: UCKL1 expression partly contributes to EUrd cytotoxicity and positively regulates UMP synthesis in resistant glioblastoma-initiating cells.
supporting_text: >-
We demonstrate that the cytotoxic effect of EUrd on GICRs partly depended
on the increased expression of uridine-cytidine kinase-like 1 (UCKL1) and
the decreased one of 5'-nucleotidase cytosolic III (NT5C3), which regulate
uridine-monophosphate synthesis positively and negatively respectively.
reference_section_type: ABSTRACT
full_text_unavailable: true
reference_review:
relevance: MEDIUM
correctness: VERIFIED
review_notes: >-
PMID and title were checked. The abstract-only evidence supports a
context-specific role in EUrd action, not a general additional substrate
annotation without the inaccessible assay details.
- id: PMID:32083188
title: Uridine Cytidine Kinase Like-1 Enhances Tumor Cell Proliferation and Mediates Protection from Natural Killer-Mediated Killing.
findings:
- statement: UCKL1 overexpression increases proliferation and protects tumor cells from NK- and drug-induced apoptosis.
supporting_text: We show that UCKL-1 over-expression protects tumor cells from NK-mediated and drug-induced apoptosis, enhances tumor survival in vitro and in vivo and increases the rate of tumor cell proliferation.
reference_section_type: INTRODUCTION
- statement: UCKL1 abundance correlates with NF-kappaB activity in K562 cells.
supporting_text: UCKL-1 transfected K562 cells had significantly higher NF-ÎșB activity than control transfected cells; siUCKL-1 treated K562 cells had less NF-ÎșB activity (Figure 7a).
reference_section_type: RESULTS
reference_review:
relevance: MEDIUM
correctness: VERIFIED
review_notes: >-
PMID, title, and full text were checked. The tumor-cell phenotypes are
direct but rely substantially on overexpression and do not establish
whether kinase activity is required.
- id: PMID:39592843
title: Glucose limitation protects cancer cells from apoptosis induced by pyrimidine restriction and replication inhibition.
findings:
- statement: Deleting UCKL1 in UCK1/UCK2-deficient Jurkat cells eliminated residual uridine rescue, genetically supporting a contribution to uridine salvage.
supporting_text: >-
We therefore generated a cell line also lacking the predicted UCK, UCKL1
(UCK tKO), and observed that uridine was unable to rescue the effects of
de novo pyrimidine synthesis inhibition on proliferation and Chk1
phosphorylation, confirming the absence of UCK activity (Fig. 3c and
Extended Data Fig. 4d).
reference_section_type: RESULTS
reference_review:
relevance: MEDIUM
correctness: VERIFIED
review_notes: >-
PMID, title, and full text were checked. The result is strong independent
genetic corroboration of residual UCKL1-dependent salvage, but the
triple-knockout design does not quantify UCKL1 alone.
- id: PMID:41457201
title: Uridine-Cytidine Kinase 2 (UCK2)/Uridine-Cytidine Kinase Like 1 (UCKL1) complex exacerbates the differentiation of myocardial fibroblasts via TRIM21/Smurf2/Smad3 pathway after myocardial infarction.
findings:
- statement: Endogenous UCK2 and UCKL1 associate in human cardiac fibroblasts and mouse myocardium.
supporting_text: To experimentally validate this putative interaction, we conducted co-immunoprecipitation (Co-IP) assays, confirming that endogenous UCK2 physically associates with UCKL1 in both HCFs and myocardial tissues (Fig. 2b, c).
reference_section_type: RESULTS
- statement: UCK2 and UCKL1 cooperatively promote TGF-beta-mediated cardiac fibroblast differentiation.
supporting_text: Collectively, these results establish UCK2 and UCKL1 as critical, potentially cooperative drivers of TGF-ÎČ-mediated HCF differentiation.
reference_section_type: RESULTS
- statement: Kinase-dead UCK2/UCKL1 proteins retained the reported profibrotic activity.
supporting_text: Strikingly, the loss of kinase activity did not abolish their pro-fibrotic potential, as indicated by the sustained upregulation of fibrogenic markers and HCFs proliferation (Fig. S3).
reference_section_type: RESULTS
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
PMID, title, and full text were checked. This is a recent, direct,
multi-level study of a context-specific kinase-independent scaffold role,
but it is currently a single report and is not elevated to a core evolved
function pending independent replication.
- id: Reactome:R-HSA-73614
title: Pyrimidine salvage
findings:
- statement: Reactome defines the human pyrimidine-salvage pathway that contains the UCKL1 event.
supporting_text: >-
In pyrimidine salvage reactions, nucleosides and free bases generated by
DNA and RNA breakdown are converted back to nucleotide monophosphates,
allowing them to re-enter the pathways of pyrimidine biosynthesis and
interconversion.
reference_review:
relevance: MEDIUM
correctness: VERIFIED
review_notes: >-
The cached Reactome record and stable identifier were checked. It provides
pathway context rather than UCKL1-specific experimental evidence.
- id: Reactome:R-HSA-8954327
title: UCKL1 phosphorylates urindine, cytidine
findings:
- statement: Reactome places UCKL1 in the cytosol and models uridine/cytidine phosphorylation.
supporting_text: >-
Based on sequence similarity, cytosolic uridine-cytidine kinase-like 1
(UCKL1 aka F538) is thought to function as a novel human uridine
kinase/uracil phosphoribosyltransferase (Kashuba et al. 2002).
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
The cached Reactome record and stable identifier were checked. The event
correctly records the historical sequence-based inference and cytosolic
placement; direct 2022 evidence now confirms kinase activity, while UPRT
activity remains untested.
- id: file:human/UCKL1/UCKL1-uniprot.txt
title: UniProt record for human UCKL1 (Q9NWZ5)
findings:
- statement: Reviewed UniProt curates direct uridine and cytidine phosphorylation by UCKL1.
supporting_text: Phosphorylates uridine and cytidine to uridine monophosphate and cytidine monophosphate.
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
The complete local reviewed UniProt record (entry version 187) was
inspected, including function, reactions, kinetics, isoforms, localization,
interactions, domains, and sequence features.
core_functions:
- description: >-
Phosphorylates uridine with ATP to produce UMP, supporting pyrimidine
nucleoside salvage and the complete UMP salvage reaction.
molecular_function:
id: GO:0004849
label: uridine kinase activity
directly_involved_in:
- id: GO:0044206
label: UMP salvage
- id: GO:0043097
label: pyrimidine nucleoside salvage
locations:
- id: GO:0005737
label: cytoplasm
substrates:
- id: CHEBI:16704
label: uridine
supported_by:
- reference_id: PMID:35583288
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
- reference_id: PMID:39592843
supporting_text: >-
We therefore generated a cell line also lacking the predicted UCK, UCKL1
(UCK tKO), and observed that uridine was unable to rescue the effects of
de novo pyrimidine synthesis inhibition on proliferation and Chk1
phosphorylation, confirming the absence of UCK activity (Fig. 3c and
Extended Data Fig. 4d).
reference_section_type: RESULTS
- description: >-
Phosphorylates cytidine with ATP to produce CMP, providing the first step of
CTP salvage from cytidine.
molecular_function:
id: GO:0043771
label: cytidine kinase activity
directly_involved_in:
- id: GO:0044211
label: CTP salvage
- id: GO:0043097
label: pyrimidine nucleoside salvage
locations:
- id: GO:0005737
label: cytoplasm
substrates:
- id: CHEBI:17562
label: cytidine
supported_by:
- reference_id: PMID:35583288
supporting_text: Both enzymes efficiently phosphorylated uridine and cytidine (Figure 3).
reference_section_type: RESULTS
proposed_new_terms: []
suggested_questions:
- question: >-
Does the C-terminal phosphoribosyltransferase-like domain of human UCKL1
catalyze PRPP-dependent uracil phosphoribosyltransferase activity under any
physiological condition?
experts:
- Elise C. Matchett
- Elise C. Ambrose
- Jacki Kornbluth
- Elena Kashuba
- question: >-
Are the tumor-cell survival, NF-kappaB, and nucleoside-analogue phenotypes
caused by UCKL1 kinase activity, by a kinase-independent scaffold function,
or by both?
experts:
- Elise C. Ambrose
- Jacki Kornbluth
- Richard G. Hoover
- question: >-
Is the reported kinase-independent nuclear UCK2-UCKL1-TRIM21 scaffold a
reproducible endogenous mechanism in human post-infarction cardiac
fibroblasts, and which UCKL1 interface is required?
experts:
- Xiao Zhou
- Yu Zhang
- Yongyi Wang
- question: >-
Which UCKL1 splice isoforms retain nucleoside kinase activity, and how do
their C-terminal differences control EBNA3-, RNF19B-, or TGF-beta-dependent
localization and turnover?
experts:
- Elena Kashuba
- Jacki Kornbluth
suggested_experiments:
- experiment_type: Purified-enzyme biochemistry
description: >-
Assay full-length UCKL1 and isolated or active-site-mutated C-terminal
domains for conversion of uracil plus PRPP to UMP using orthogonal
LC-MS-based product detection and appropriate active UPRT controls.
hypothesis: >-
The UPRT-like C-terminal domain is either catalytically active only under
specific cofactor or oligomerization conditions, or is a catalytically
inactive structural domain.
- experiment_type: Catalytic-dead endogenous rescue and isotope tracing
description: >-
Create UCKL1-null human cells and rescue them at endogenous abundance with
wild-type or kinase-dead UCKL1, then quantify labeled uridine and cytidine
flux into UMP/CMP/UTP/CTP together with proliferation, apoptosis, NF-kappaB
activity, and NK-cell killing.
hypothesis: >-
Pyrimidine-salvage flux requires UCKL1 kinase activity, whereas some
survival or signaling phenotypes persist with catalytically inactive UCKL1.
- experiment_type: Isoform-resolved endogenous localization
description: >-
Tag individual endogenous UCKL1 isoforms and follow their localization,
interaction, ubiquitination, and half-life after EBNA3 expression, RNF19B
induction, or TGF-beta activation without overexpression.
hypothesis: >-
The C-terminal region controls partner-specific nuclear trafficking and
degradation independently of the shared N-terminal nucleoside-kinase domain.
- experiment_type: Independent cardiac-fibroblast mechanism replication
description: >-
Reproduce the UCK2-UCKL1-TRIM21-Smurf2/SMAD3 mechanism with orthogonal
endogenous proximity labeling, separation-of-function interface mutants,
kinase-dead knock-in rescue, and fibroblast-specific loss and rescue in a
second myocardial-infarction model.
hypothesis: >-
UCKL1 has a genuine kinase-independent scaffold activity in activated
cardiac fibroblasts that is separable from pyrimidine salvage.