REL1 (TbMP52, RNA-editing ligase 1) — Trypanosoma brucei TREU927 — curation notes

Automated deep research was unavailable in this environment (Falcon auth failure, invalid OpenAI key). These notes are a manual literature review based on the UniProt record (P86927), the cached publications cited in GOA, and additional primary papers located by web search and verified against PubMed before caching.

Identity

• UniProt P86927 (RLGM1_TRYB2), 469 aa, gene REL1, synonym MP52 / TbMP52, TriTrypDB Tb927.9.4360. N-terminal mitochondrial transit peptide 1..44 (UniProt FT TRANSIT). Belongs to the RNA ligase 2 (Rnl2) family (InterPro IPR012647 RNA_lig_RNL2), the nucleotidyltransferase superfamily shared with DNA ligases and mRNA capping enzymes; active-site lysine K87 forms the covalent ligase-AMP intermediate.
• Paralog REL2 (TbMP48) sits in the insertion subcomplex; REL1 sits in the deletion subcomplex.

Function

• Identified as a component of the ~1,600 kDa editosome: PMID:11134327 The purified complex PMID:11134327.
• RNA ligase activity and essentiality: PMID:11251122 and PMID:11251122; lethal in bloodstream forms PMID:11251122
• Structure: 1.2 A crystal structure of the catalytic domain with ATP and Mg2+ PMID:15465048; REL1 is essential in both life stages PMID:15465048; no close human homolog PMID:15465048.
• Deletion subcomplex: PMID:14536071; PMID:14536071

Localization

• Mitochondrion (transit peptide; editosome purified from mitochondria PMID:11134327). MitoCarta SVM prediction PMID:20660476.
• TrypTag (GO_REF:0000109) gave kinetoplast and cytoplasm calls. Cytoplasm in GO includes the mitochondrion, so it is true but uninformative; a cytosolic signal could also be an N-terminal-tag artefact masking the transit peptide. Kinetoplast (sub-mitochondrial region around kDNA) is plausible given editing of maxicircle transcripts but the core site is the mitochondrial matrix.
• Complex map: REL1 was the bait in a TEV-elution pulldown PMID:26991453; PMID:26991453.

Curation decisions (summary)

• Ligase activity (IEA) -> MODIFY to RNA ligase (ATP) activity GO:0003972 (already present; experimentally supported).
• RNA modification (IDA, IEA) -> MODIFY to mitochondrial mRNA modification GO:0080156 (OLS-verified; child of mRNA modification and mitochondrial RNA modification). GO merged "RNA editing" into "RNA modification"; U-insertion/deletion editing has no dedicated term.
• Cytoplasm (TrypTag IDA) -> MODIFY to mitochondrion.
• Editosome GO:0031019, mitochondrion, RNA ligase (ATP) activity -> ACCEPT. Kinetoplast -> KEEP_AS_NON_CORE. ATP binding -> KEEP_AS_NON_CORE.
• Protist checks: no animal/plant-only terms; no host-process terms; no paralog over-annotation (REL1 vs REL2 subcomplex distinction is not represented in GO and needs no term).