PIK1 (P39104, YNL267W) notes

Evidence journal (YeastPathways phosphoinositide_biosynthesis batch, 2026-10-06).

Activity

• Type III PI 4-kinase (PI4KB ortholog) [UniProt:P39104 "Type III PI4K"].
• Encodes PI 4-kinase essential for growth PMID:8194527; overexpression raises activity PMID:8248783.
• Stt4 and Pik1 have the same biochemical activity but are non-redundant PMID:10930462; each single ts mutant halves PtdIns4P, double >10-fold PMID:10930462.
• YeastPathways step PI + ATP -> PI4P (EC 2.7.1.67) is correct.

Location

• TGN and nucleus PMID:16365163; both pools needed PMID:16365163.
• Golgi recruitment by Frq1 PMID:16365163 and Gga2 PMID:22344030.

Processes

• Golgi secretion PMID:10930462.
• Autophagy / microautophagy roles are downstream lipid requirements PMID:31125705.

Curation decisions

• RCA cytosol -> MODIFY to TGN; generic kinase IEA -> MODIFY to GO:0004430; protein binding (Frq1, Gga2) REMOVE as uninformative; ARBA 'cellular response to stress' over-annotated.
• PMID:10587649 not available (no abstract in cache); its IDA/IMP rows accepted because consistent with other evidence.

Description follow-up (UniProt/SGD text)

• Pheromone response: the only evidence is an overexpression phenotype PMID:8248783. Checked and peripheral; not annotated.
• Cytokinesis: conditional mutants arrest with large buds and divided nuclei, and the actin link was a suggestion PMID:8194527. Given the later Golgi secretion defect PMID:10930462, the cytokinesis arrest may be secondary to loss of Golgi PtdIns4P. Not annotated.
• Neither UniProt nor SGD mentions the Golgi PtdIns4P requirement for secretory cargo exit or the Frq1 subunit; recorded as MISSING_STATEMENT on both cited source texts.