ACL4

UniProt ID: Q03771
Organism: Saccharomyces cerevisiae
Review Status: COMPLETE
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Gene Description

ACL4 encodes a dedicated assembly chaperone for the large ribosomal subunit protein Rpl4/uL4. Acl4 captures nascent Rpl4, shields its extended basic internal loop, keeps unassembled Rpl4 soluble, and accompanies it from the cytoplasm to nuclear pre-60S assembly sites. Loss of ACL4 causes slow growth, reduced 60S subunit production, half-mer polysomes and pre-rRNA processing defects.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0005741 mitochondrial outer membrane
IBA
GO_REF:0000033
UNDECIDED
Summary: The mitochondrial inference remains unresolved after correcting the overly strong exclusion rationale.
Reason: The IBD at PTN002340064 is a genuine TOM70-family ancestral assertion. Primary Acl4 studies establish a soluble Rpl4-specific chaperone pathway but do not test or exclude every mitochondrial client interaction or peripheral membrane contribution. The existing report neither reconstructs the PAINT topology nor demonstrates target-specific loss of these particular activities. Its use of absent transmembrane helices as universal refutation is insufficient for a peripheral factor or complex contribution.
Propagation Review
Root cause: UNRESOLVED
Sources checked:
PANTHER:PTN002340064 · PTN002340064 UNRESOLVED
Current PTHR46208 PAINT IBDs confirm mitochondrial outer-membrane/import/insertion and transporter assertions. The report does not establish a misplaced target branch, and lack of an integral-membrane segment does not refute soluble or contributes_to participation.
Supporting Evidence:
PMID:26447800
Acl4 localizes to both the cytoplasm and nucleus
file:yeast/ACL4/ACL4-hypotheses/function-hypothesis-go-0008320/openscientist.md
**zero** transmembrane-candidate segments
GO:0008320 protein transmembrane transporter activity
IBA
GO_REF:0000033
UNDECIDED
Summary: The mitochondrial inference remains unresolved after correcting the overly strong exclusion rationale.
Reason: The IBD at PTN002340064 is a genuine TOM70-family ancestral assertion. Primary Acl4 studies establish a soluble Rpl4-specific chaperone pathway but do not test or exclude every mitochondrial client interaction or peripheral membrane contribution. The existing report neither reconstructs the PAINT topology nor demonstrates target-specific loss of these particular activities. Its use of absent transmembrane helices as universal refutation is insufficient for a peripheral factor or complex contribution. This row is explicitly contributes_to: it does not assert that Acl4 itself forms a membrane-spanning channel. Rpl4 nuclear-pore passage does not by itself establish mitochondrial transmembrane transport either.
Propagation Review
Root cause: UNRESOLVED
Sources checked:
PANTHER:PTN002340064 · PTN002340064 UNRESOLVED
Current PTHR46208 PAINT IBDs confirm mitochondrial outer-membrane/import/insertion and transporter assertions. The report does not establish a misplaced target branch, and lack of an integral-membrane segment does not refute soluble or contributes_to participation.
Supporting Evidence:
PMID:26447800
Acl4 localizes to both the cytoplasm and nucleus
file:yeast/ACL4/ACL4-hypotheses/function-hypothesis-go-0008320/openscientist.md
**zero** transmembrane-candidate segments
GO:0030150 protein import into mitochondrial matrix
IBA
GO_REF:0000033
UNDECIDED
Summary: The mitochondrial inference remains unresolved after correcting the overly strong exclusion rationale.
Reason: The IBD at PTN002340064 is a genuine TOM70-family ancestral assertion. Primary Acl4 studies establish a soluble Rpl4-specific chaperone pathway but do not test or exclude every mitochondrial client interaction or peripheral membrane contribution. The existing report neither reconstructs the PAINT topology nor demonstrates target-specific loss of these particular activities. Its use of absent transmembrane helices as universal refutation is insufficient for a peripheral factor or complex contribution.
Propagation Review
Root cause: UNRESOLVED
Sources checked:
PANTHER:PTN002340064 · PTN002340064 UNRESOLVED
Current PTHR46208 PAINT IBDs confirm mitochondrial outer-membrane/import/insertion and transporter assertions. The report does not establish a misplaced target branch, and lack of an integral-membrane segment does not refute soluble or contributes_to participation.
Supporting Evidence:
PMID:26447800
Acl4 localizes to both the cytoplasm and nucleus
file:yeast/ACL4/ACL4-hypotheses/function-hypothesis-go-0008320/openscientist.md
**zero** transmembrane-candidate segments
GO:0030943 mitochondrion targeting sequence binding
IBA
GO_REF:0000033
UNDECIDED
Summary: The mitochondrial inference remains unresolved after correcting the overly strong exclusion rationale.
Reason: GO:0030943 (mitochondrion targeting sequence binding) is obsolete in the current GO release (consider GO:0140436 / GO:0008320). No replacement is proposed while the underlying PAINT inference remains unresolved. The IBD at PTN002340064 is a genuine TOM70-family ancestral assertion. Primary Acl4 studies establish a soluble Rpl4-specific chaperone pathway but do not test or exclude every mitochondrial client interaction or peripheral membrane contribution. The existing report neither reconstructs the PAINT topology nor demonstrates target-specific loss of these particular activities. Its use of absent transmembrane helices as universal refutation is insufficient for a peripheral factor or complex contribution. The targeting-sequence-binding assertion is present in the original GOA but absent from the newer PTHR46208 PAINT table; a version difference is not biological refutation.
Propagation Review
Root cause: UNRESOLVED
Sources checked:
PANTHER:PTN002340064 · PTN002340064 UNRESOLVED
The current PTHR46208 PAINT table contains mitochondrial membrane/import assertions but does not contain GO:0030943. This historical source assertion remains unresolved; absence from the newer snapshot is not itself evidence of biological loss.
Supporting Evidence:
PMID:26447800
Acl4 localizes to both the cytoplasm and nucleus
file:yeast/ACL4/ACL4-hypotheses/function-hypothesis-go-0008320/openscientist.md
**zero** transmembrane-candidate segments
GO:0045039 protein insertion into mitochondrial inner membrane
IBA
GO_REF:0000033
UNDECIDED
Summary: The mitochondrial inference remains unresolved after correcting the overly strong exclusion rationale.
Reason: The IBD at PTN002340064 is a genuine TOM70-family ancestral assertion. Primary Acl4 studies establish a soluble Rpl4-specific chaperone pathway but do not test or exclude every mitochondrial client interaction or peripheral membrane contribution. The existing report neither reconstructs the PAINT topology nor demonstrates target-specific loss of these particular activities. Its use of absent transmembrane helices as universal refutation is insufficient for a peripheral factor or complex contribution.
Propagation Review
Root cause: UNRESOLVED
Sources checked:
PANTHER:PTN002340064 · PTN002340064 UNRESOLVED
Current PTHR46208 PAINT IBDs confirm mitochondrial outer-membrane/import/insertion and transporter assertions. The report does not establish a misplaced target branch, and lack of an integral-membrane segment does not refute soluble or contributes_to participation.
Supporting Evidence:
PMID:26447800
Acl4 localizes to both the cytoplasm and nucleus
file:yeast/ACL4/ACL4-hypotheses/function-hypothesis-go-0008320/openscientist.md
**zero** transmembrane-candidate segments
GO:0005634 nucleus
IEA
GO_REF:0000044
ACCEPT
Summary: UniProt subcellular-location mapping to nucleus is consistent with direct Acl4 localization studies and with Acl4 delivery of Rpl4 to nuclear pre-60S particles.
Reason: Acl4 is enriched in the nucleus and performs its client-delivery function at the nuclear pre-60S assembly site.
GO:0005737 cytoplasm
IEA
GO_REF:0000120
ACCEPT
Summary: Automated cytoplasm assignment is consistent with direct studies showing Acl4 in the cytoplasm, where Rpl4 is synthesized and first captured.
Reason: Cytoplasmic localization is part of the supported escort path from nascent Rpl4 capture to nuclear assembly.
GO:0042254 ribosome biogenesis
IEA
GO_REF:0000043
ACCEPT
Summary: The keyword-derived ribosome biogenesis term is broad but accurate for Acl4, which is required for efficient production of 60S ribosomal subunits.
Reason: Experimental annotations to ribosomal large subunit biogenesis provide the more specific evidence; this parent process is correct as an automated summary of Acl4 function.
GO:0005634 nucleus
IDA
PMID:25936803
Coordinated Ribosomal L4 Protein Assembly into the Pre-Ribos...
ACCEPT
Summary: Direct experimental localization supports nuclear Acl4, consistent with the Rpl4 pre-60S assembly site.
Reason: The localization matches the mechanistic model in which Acl4 delivers Rpl4 to nuclear pre-60S assembly intermediates.
Supporting Evidence:
PMID:25936803
assembly chaperone Acl4 that initially binds the universally conserved internal
GO:0005634 nucleus
IDA
PMID:26447800
The Dedicated Chaperone Acl4 Escorts Ribosomal Protein Rpl4 ...
ACCEPT
Summary: Direct microscopy in the dedicated Acl4-Rpl4 study supports nuclear localization.
Reason: Acl4 localizes to the nucleus as expected for a factor escorting Rpl4 to nuclear pre-60S assembly sites.
Supporting Evidence:
PMID:26447800
Acl4 localizes to both the cytoplasm and nucleus
GO:0005737 cytoplasm
IDA
PMID:26447800
The Dedicated Chaperone Acl4 Escorts Ribosomal Protein Rpl4 ...
ACCEPT
Summary: Direct microscopy supports cytoplasmic Acl4 localization.
Reason: Acl4 must encounter newly translated Rpl4 in the cytoplasm before nuclear delivery, so this localization is mechanistically coherent.
Supporting Evidence:
PMID:26447800
Acl4 localizes to both the cytoplasm and nucleus
GO:0042273 ribosomal large subunit biogenesis
IMP
PMID:25936803
Coordinated Ribosomal L4 Protein Assembly into the Pre-Ribos...
ACCEPT
Summary: Mutant phenotype evidence shows that ACL4 is required for normal 60S subunit production through Rpl4 assembly.
Reason: Acl4 shields Rpl4 until it can be inserted into the pre-ribosome; ACL4 loss causes large-subunit biogenesis defects, making this a core process.
Supporting Evidence:
PMID:25936803
hierarchical ribosome assembly can be achieved by eukaryotic RP extensions and
GO:0042273 ribosomal large subunit biogenesis
IMP
PMID:26447800
The Dedicated Chaperone Acl4 Escorts Ribosomal Protein Rpl4 ...
ACCEPT
Summary: The dedicated chaperone study shows that Acl4 escorts Rpl4 to its nuclear pre-60S assembly site and that loss of Acl4 compromises 60S production.
Reason: This is the central biological process for Acl4 and is supported by genetic, localization, and biochemical evidence.
Supporting Evidence:
PMID:26447800
deficiency in the production of 60S subunits
GO:0051082 unfolded protein binding
IDA
PMID:25936803
Coordinated Ribosomal L4 Protein Assembly into the Pre-Ribos...
MODIFY
Summary: The obsolete unfolded-protein-binding term is best represented by the dedicated carrier-chaperone activity.
Reason: Live QuickGO marks GO:0051082 obsolete. Primary Acl4/Rpl4 studies demonstrate client shielding and escort to pre-60S assembly, supporting GO:0140597 protein carrier chaperone as the specific replacement.
Proposed replacements: protein carrier chaperone
Supporting Evidence:
PMID:26447800
dedicated chaperone Acl4 accompanies Rpl4
GO:0140318 protein transporter activity
IDA
PMID:26447800
The Dedicated Chaperone Acl4 Escorts Ribosomal Protein Rpl4 ...
ACCEPT
Summary: The evidence supports Acl4 directly binding and escorting Rpl4 to the pre-60S assembly pathway, matching the current definition of protein transporter activity as binding and delivering a specific protein to a cellular location.
Reason: QuickGO places GO:0140318 under transporter activity and GO:0140597 under molecular carrier activity rather than as a parent-child pair. Retaining this SGD IDA annotation is therefore not a redundant parent annotation, and the PMID:26447800 evidence supports Acl4 escorting Rpl4 to the pre-60S assembly pathway.
Supporting Evidence:
PMID:26447800
dedicated chaperone Acl4 accompanies Rpl4
GO:0051083 'de novo' cotranslational protein folding
HGI
PMID:19325107
Comprehensive characterization of genes required for protein...
UNDECIDED
Summary: Cotranslational Rpl4 capture is demonstrated, while the precise folding contribution in the HGI source remains unresolved.
Reason: GO:0051083 concerns correct noncovalent assembly of nascent chains while translation continues, and does not imply a general chaperone for all substrates. PMID:26447800 directly supports cotranslational Rpl4 recognition, but recognition/protection need not itself demonstrate the folding step. The cached PMID:19325107 remains abstract-only after full-text retrieval attempts; its ACL4 genetic-interaction evidence should not be overruled from the abstract or the preference for a more specific carrier role.
Supporting Evidence:
PMID:26447800
We conclude that Acl4 has the capacity to recognize Rpl4 in a co-translational manner.
GO:0005634 nucleus
HDA
PMID:14562095
Global analysis of protein localization in budding yeast.
ACCEPT
Summary: High-throughput localization to nucleus is consistent with direct Acl4 localization and its nuclear pre-60S assembly role.
Reason: Multiple independent sources support nuclear localization.
GO:0005737 cytoplasm
HDA
PMID:14562095
Global analysis of protein localization in budding yeast.
ACCEPT
Summary: High-throughput localization to cytoplasm is consistent with direct Acl4 localization and nascent Rpl4 capture.
Reason: Acl4 is distributed through cytoplasm and nucleus, matching its escort function.

Core Functions

Acl4 is a dedicated carrier chaperone for Rpl4/uL4. It binds newly synthesized Rpl4 in the cytoplasm, protects it from inappropriate interactions or aggregation, and escorts it to nuclear pre-60S particles for large ribosomal subunit assembly.

Molecular Function:
protein carrier chaperone
Cellular Locations:
Supporting Evidence:
  • PMID:26447800
    dedicated chaperone Acl4 accompanies Rpl4
  • file:yeast/ACL4/ACL4-deep-research-falcon.md
    Acl4 binds newly synthesized, free Rpl4

References

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Suggested Questions for Experts

Q: Does ACL4 have a secondary mitochondrial client-binding or transporter-complex role, and does the actual PAINT topology support inheritance at PTN002340064?

Q: Does nascent Rpl4 binding actively assist its noncovalent folding, or chiefly shield an extended loop until ribosomal incorporation?

Suggested Experiments

Experiment: Re-analyze ACL4, TOM70, and related PTHR46208 subfamilies with tree-aware GO propagation to test whether mitochondrial import annotations segregate away from the experimentally characterized Acl4/Rpl4 clade.

Hypothesis: The ACL4 subfamily lacks the mitochondrial protein import functions present in TOM70-like relatives and should not inherit those IBA terms.

Type: phylogenetic curation

Deep Research

Falcon

(ACL4-deep-research-falcon.md)

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OpenScientist

(ACL4-hypotheses/function-hypothesis-go-0008320/openscientist.md)

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OpenScientist

(ACL4-hypotheses/mitochondrial-targeting-and-translocation-contribution/openscientist.md)

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📚 Additional Documentation

Notes

(ACL4-notes.md)

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📄 View Raw YAML

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