Pig1p is a putative targeting subunit for the type-1 protein phosphatase Glc7p that tethers it to the Gsy2p glycogen synthase (1, 3). Pig1p binds Gsy2p in two-hybrid analyses, and PIG1 displays overall similarity to GAC1, suggesting that Pig1p may functionally overlap Gac1p, which also tethers Glc7p to Gsy2p, in glycogen biosynthesis (1).

pig1 gac1 double null mutants display decreased glycogen accumulation compared to either gac1 null mutants or wild type (1). glc7-109 mutants display increased levels of glycogen compared to wild type, and this hyperglycogen phenotype is partially retained in pig1 gac1 gip2 triple null glc7-109 mutants, indicating there may be other targeting subunits capable of targeting Glc7p-109 to Gsy2p (3). The growth of pig1 ppz1 ppz2 triple null mutants appears identical to that of ppz1 ppz2 double null mutants, indicating that there are no genetic interactions between PIG1 and PPZ1 and PPZ2, both of which encode Glc7p-related protein phosphatases (4).

Pig1p, Gac1p, Pig2p and Gip2p are the only four proteins in S. cerevisiae that share a conserved segment of 25 residues, designated the GVNK motif, which is conserved in mammalian type-1 phosphatase targeting subunits (1). Pig1p also has regions of similarity to the Rhizopus glucoamylase precursor AMYG, and also to various mammalian glycogen-associated regulatory subunits of protein phosphatase 1 (1), including rabbit RG RAB and human PPP1R3, mutations in which are associated with non-insulin-dependent diabetes mellitus (5).

Last updated: 2005-10-20