OPI3 (PEM2, YJR073C, P05375) notes

Identity

• Phospholipid N-methyltransferase (PLMT), EC 2.1.1.71 (minor 2.1.1.17); PEMT family; ER multi-pass membrane protein [UniProt:P05375].

Evidence

• PEM2 membranes convert PE to PC; prefer PMME/PDME PMID:2445736.
• pem2 disruption loses 2nd and 3rd methylations PMID:2684666
• PLMT kinetics in cho2 disruptants PMID:2198947.
• opi3-3 mutant: 2-3% PC without choline, accumulates PMME/PDME PMID:6337128
• PE-methylation activity microsomal PMID:3005242.

Curation decisions

• Core: GO:0000773 + PC biosynthesis at ER membrane. GO:0004608 (first methylation) non-core (minor, Cho2 is main enzyme).
• Mitochondrial / cell-periphery HDA/EXP kept non-core (likely contact-site association). Cytosol RCA removed.