SUMMARY PARAGRAPH for PHO2
PHO2, also known as BAS2 or GRF10, encodes a homeodomain transcriptional activator that activates transcription in a combinatorial manner (3,2). Pho2p is required to express genes in several different pathways such as purine nucleotide biosynthesis, histidine biosynthesis, and phosphate utilization (6). Genes that are known to be regulated by Pho2p include PHO5, PHO81, HIS4, CYC1, TRP4, HO, ADE1, ADE2, ADE5,7 and ADE8 (4). Although purified Pho2p has been shown in vitro to have low affinity DNA binding activity, in vivo, it activates transcription along with one of at least three distinct partner proteins: the zinc finger protein Swi5p (7), the basic-helix-loop-helix factor Pho4p (8), and Bas1p, a myb-like activator (6). Pho2p and Pho4p cooperatively bind to the promoter site of PHO5 (which encodes for a secreted acid phosphatase) and are required for PHO5 expression when cells are starved of phosphate (9). Pho2p and Swi5p together activate HO, while Pho2p and Bas1p activate genes in the purine and histidine biosynthesis pathways (9). Pho2p is phosphorylated by cdc2/CDC28-type kinase at the 'SPIK' site (amino acids 230-233). This phosphorylation of Pho2p facilitates the interaction between Pho2p and Pho4p which is required for PHO5 expression under low phosphate conditions. Deletion and point mutation analyses have revealed that the homeodomain (amino acids 77-136) is necessary but not sufficient for cooperative DNA binding, and that a large C-terminal region (amino acids 112-404), including the Pho80p homologous region (amino acids 241-258), is required for interaction with its partners Swi5p, Pho4p, and Bas1p (4).
Last updated: 2003-03-13