IPT1 (YDR072C) notes

UniProt P38954, M(IP)2C synthase (inositolphosphotransferase 1; EC 2.7.1.228), AUR1-family multipass Golgi membrane protein [UniProt:P38954].

• PMID:9368028; membranes from ipt1 lack M(IP)2C synthase activity PMID:9368028.
• Membrane activity transferring PI-inositol phosphate to sphingolipid PMID:6991492.
• Golgi (EXP, PMID:14583628; abstract only mentions Csg1/Csh1 co-localising with IPC synthase in medial Golgi; deferred to curator).
• With SKN1, required for M(IP)2C and DmAMP1 sensitivity PMID:15792805; ipt1 skn1 double mutant has increased autophagy PMID:20030721.

GO term gap

• No GO MF for MIPC + PI -> M(IP)2C + DAG (EC 2.7.1.228, RHEA:64540). Existing rows use "transferase activity, transferring phosphorus-containing groups". Proposed new term.
• Note: GO:0045140 (IPC synthase, Aur1) is placed is_a GO:0016758 hexosyltransferase activity, which is chemically wrong (it is a phosphoinositol transfer) - ontology issue relevant to AUR1/IPT1.

Pathway context

• YeastPathways reaction for IPT1 (MIPC + PI -> M(IP)2C) correct. RCA cytosol wrong (Golgi membrane enzyme).
• IBA "inositol phosphoceramide synthase complex" propagated from Aur1 (Aur1-Kei1) to its paralog Ipt1: not supported.