High impact information on PHO2

• The yeast regulatory gene PHO2 encodes a homeo box [1].
• Similarly, we find that low levels of transcription by Bas1/Bas2 are TATA-independent, whereas high levels are TATA-dependent [2].
• Phosphorylation of a fourth site blocks the interaction of Pho4 with the transcription factor Pho2 [3].
• Induction of the yeast gene PHO5 is mediated by the transcription factors PHO2 and PHO4 [4].
• BAS1 has a Myb motif and activates HIS4 transcription only in combination with BAS2 [5].

Biological context of PHO2

• Genetic mapping and DNA sequence analysis show that BAS2 is PHO2, a gene previously identified as a regulator of phosphate metabolism [6].
• It has been shown previously that point mutations in either Swi5p binding site only modestly reduce HO expression in a PHO2 strain [7].
• The yeast PHO2 gene encodes a homeodomain protein that exemplifies combinatorial control in transcriptional activation [8].
• SW15 encodes a zinc finger DNA binding protein required for the transcription of the Saccharomyces cerevisiae HO gene, and PHO2 encodes a homeodomain DNA binding protein [9].
• N-terminal amino acid sequence analysis identified the Swi5 stimulatory factor as the product of the GRF10 gene, which encodes a yeast homeodomain protein [10].

Anatomical context of PHO2

• The vacuole inheritance defect in vac5-1 cells is dependent on the presence of the Pho85 kinase and its targets Pho4p and Pho2p [11].

Associations of PHO2 with chemical compounds

• These results suggest that glycine affects Bas1p activation of transcription rather than DNA binding and that Bas2p is not required for this affect [12].
• The transcription factors BAS1 and BAS2/PHO2, which are also regulators of the histidine pathway, participate in the regulation of the purine biosynthetic pathway [13].
• The basal level transcription of the HIS4 gene is under the control of two genes, BAS1 and BAS2, which are also required for the control of purine biosynthesis [6].
• In contrast, a LexA-Bas1p fusion activated the lexAop reporter in a BAS2-dependent and adenine-regulated fashion [14].
• Nevertheless, a Bas2p cysteine-free mutant was not sufficient to confer resistance to oxidative stress [15].

Physical interactions of PHO2

• Grf10 protein purified from a bacterial expression system binds DNA cooperatively with Swi5 in vitro [10].
• The Swi5 zinc-finger and Grf10 homeodomain proteins bind DNA cooperatively at the yeast HO promoter [10].
• Gel retardation assays with the PHO2 protein revealed a binding region that lay between the two PHO4-binding sites [16].
• Direct biochemical analysis shows that the BAS2 gene encodes a protein that binds to both the HIS4 and PHO5 promoters [6].
• The other element shows strong sequence identity with the Bas2p binding site and appears to be involved in basal and phosphate-mediated regulation of LEU4 [17].

Regulatory relationships of PHO2

• A Bas1p-VP16 fusion protein activated expression in a bas1bas2 strain but no glycine effect was observed while a Bas1p-Bas2p fusion protein activated expression to a lesser extent with a slight stimulation by glycine [12].
• We show here that Pho4 and the homeobox protein Pho2 interact in vivo and act cooperatively to activate the PHO5 UAS, with interaction being regulated by the phosphate switch [18].
• Previous studies have shown that GIT1 expression is regulated by inorganic phosphate (P(i)) availability through the transcription factors Pho2p and Pho4p [19].
• We conclude that efficient transcription of yeast AMP biosynthesis genes requires interaction between Bas1p and Bas2p which is promoted in the presence of a metabolic intermediate whose synthesis is controlled by feedback inhibition of Ade4p acting as the purine nucleotide sensor within the cell [20].

Other interactions of PHO2

• Addition of a Bas1p-LexA fusion protein to a strain with a LexAop-LacZ fusion showed a strong glycine effect both in a BAS2 and a bas2 background [12].
• The suppression appeared to be a direct effect of PHO4, not a secondary effect of PHO regulon derepression, and was PHO2-dependent [21].
• Coordinate increases of PHO80 and PHO2 give rise to the same phenotype as an increased dosage of PHO80 alone [22].
• Absence of PHO2 reduces the basal expression of CYC1 [23].
• Sequence of the PHO2-POL3 (CDC2) region of chromosome IV of Saccharomyces cerevisiae [24].

Analytical, diagnostic and therapeutic context of PHO2

• This fragment was used to evict the genomic copy and with appropriate genetic crosses we proved, that the cloned gene is PHO2 [25].
• Final purification of the 83-kDa GRF10 protein was achieved by cooperative interaction-based DNA affinity chromatography [26].
• These data combined with LacZ fusions and northern blot analysis allow us to show that synthesis of enzymes for all 10 steps involved in purine de novo synthesis is repressed in the presence of adenine and requires BAS1 and BAS2 for optimal expression [27].
• Immunoprecipitation experiments showed that Pho4p and Pho2p form a complex on a 36-bp sequence bearing an upstream activation site (UAS) and protein binding assays indicated that these proteins interact directly [28].

References