GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

InterPro signatures IPR004033 (UbiE/COQ5_MeTrFase) and IPR023576 (UbiE/COQ5_MeTrFase_CS) map to methyltransferase activity; the UbiE/COQ5 family corresponds to the specific 2-methoxy-6-polyprenyl-1,4-benzoquinol methyltransferase activity.

GO_REF:0000033

Annotation inferences using phylogenetic trees

COQ5 functions (ubiquinone biosynthetic process, 2-methoxy-6-polyprenyl-1,4-benzoquinol methyltransferase activity) are conserved across the PANTHER PTN001297884 COQ5/UbiE phylogenetic group.

GO_REF:0000043

Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping

SwissProt keyword-derived (SPKW) annotation present in the Sept 2025 goa_uniprot_gcrp snapshot but removed from the current GOA release after GOA retired the keyword2GO pipeline for cellular organisms.
For COQ5, the "Methyltransferase" keyword mapped to the bare process term "methylation" (GO:0032259); the specific pathway and substrate context were retained instead by GO:0006744 and GO:0008425, so removal lost no biology.

GO_REF:0000044

Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt

Mitochondrial inner-membrane localization mapped from the UniProt Subcellular Location vocabulary (SL-0168).

GO_REF:0000104

Electronic Gene Ontology annotations created by transferring manual GO annotations between related proteins based on shared sequence features

Extrinsic (peripheral, matrix-side) component of the mitochondrial inner membrane, transferred by UniRule from related COQ5 proteins.

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods

Ubiquinone biosynthetic process and the specific 2-methoxy-6-polyprenyl-1,4-benzoquinol methyltransferase activity assigned by combined IEA methods (ARBA/UniRule; RHEA:28286, EC 2.1.1.201; UniPathway UPA00232).

file:ORYSJ/COQ5/COQ5-deep-research-falcon.md

Deep-research report (falcon / Edison Scientific Literature) - functional annotation of rice COQ5 (Q5JNC0).

COQ5 is the SAM-dependent C-methyltransferase (UbiE/COQ5 family) responsible for the single C-methylation of the eukaryotic CoQ ring-modification stage; the other two methylations are O-methylations catalyzed by COQ3. It acts on a prenylated benzoquinone/benzoquinol CoQ-pathway intermediate at the C2 position, producing demethoxy-coenzyme Q (DMQ).
CoQ biosynthesis occurs at the inner mitochondrial membrane; late-pathway COQ enzymes (COQ3-COQ9) are mitochondrial (matrix-localized and/or inner-membrane associated) and function within a multi-subunit COQ metabolon / CoQ synthome.
No primary rice study directly assays COQ5 (Os01g0976600/LOC_Os01g74520) activity, localization or mutant phenotype; annotation rests on evolutionary conservation plus plant evidence that Arabidopsis AtCOQ5 complements the corresponding S. pombe coq mutant.