Disease relevance of PHO80

• Each of the fusion proteins, LacZ-Pho80 and LacZ-Pho85, was produced into Escherichia coli and used as an antigen to raise antibodies in a rabbit [1].

High impact information on PHO80

• To investigate the mechanism, we replaced the PHO80 gene, a negative regulator of PHO5, by a temperature-sensitive allele [2].
• We show that phosphorylation of Pho4 by a nuclear complex of a cyclin with a cyclin-dependent kinase, Pho80-Pho85, triggers its export from the nucleus [3].
• Phosphorylation of the transcription factor PHO4 by a cyclin-CDK complex, PHO80-PHO85 [4].
• Under conditions of constitutive submaximal activation (i.e., in the absence of the negative regulator Pho80), deletion of Gcn5 determines a novel randomized nucleosomal organization across the promoter and leads to a dramatic reduction in activity [5].
• Thus, Rim15 plays a key role in G0 entry through its ability to integrate signaling from the PKA, TORC1, and Pho80-Pho85 pathways [6].

Biological context of PHO80

• Moreover, in the absence of PHO80, the corepressor, presumed to be a metabolite of Pi, did not inhibit their function in the transcriptional activation of APase [7].
• Most interestingly, under low phosphate conditions, the An-PHO80 cyclin also promotes sexual development while having a negative effect on asexual development [8].
• A centromere sequence was found downstream of the PHO80 coding region [9].
• Coordinate increases of PHO80 and PHO2 give rise to the same phenotype as an increased dosage of PHO80 alone [10].
• The 1.8 kb DNA fragment carrying the PHO80 gene was sequenced and one open reading frame large enough to encode 293 amino acids was found in the sequence [9].

Anatomical context of PHO80

• Though vac5-1 is recessive, pho80 delta or pho85 delta strains do not show a defect in vacuole inheritance, suggesting that vac5-1 is not a complete loss-of-function allele [11].
• Immunoblotting studies reveal that cytosolic AGS3 can remove G(i)alpha subunits from the membrane and sequester G(i)alpha subunits in the cytosol [12].

Associations of PHO80 with chemical compounds

• Yeast mutants permeable to dTMP (tup) were selected and two new complementation groups (tup5 and tup7) were identified [13].
• Spontaneously arising extragenic suppressors of cep1 methionine auxotrophy were also isolated; approximately one-third of them were alleles of pho80 [14].
• The tup7 mutation increased permeability to dTMP (and some other 5'-mononucleotides), but did not affect uptake of nucleosides and purine and pyrimidine bases [15].
• The auxotrophic requirement of dcd1 dmp1 tup7 strains also can be satisfied by exogenous dTMP but not deoxyuridine [16].
• The AGS3 GPR domain markedly inhibited the rates of spontaneous guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) binding to G(i)alpha and rhodopsin-stimulated GTPgammaS binding to G(t)alpha [17].

Physical interactions of PHO80

• Pho81 forms a stable complex with Pho80-Pho85 under both high- and low-phosphate conditions, but it only inhibits the kinase when cells are starved for phosphate [18].
• Here, we show that the poorly characterized Pho80-like protein Pcl7 forms a functional kinase complex with the Pho85 cdk, and that the activity of this complex is inhibited in response to phosphate starvation [19].
• It further showed two sites on the Pho80 cyclin for high-affinity binding of the transcription factor substrate (Pho4) and the CDK inhibitor (Pho81) that are markedly distant to each other and the active site [20].

Enzymatic interactions of PHO80

• The PHO80 protein was found to be phosphorylated in the presence of PHO85 protein [1].
• Recent studies in our laboratory showed that Pho81p is phosphorylated by the Pho80p-Pho85p CDK complex in vitro; and, to determine the significance of the phosphorylation, we used site-directed mutagenesis to alter the potential phosphorylation sites for this kinase complex [21].

Regulatory relationships of PHO80

• More detailed investigation of APase synthesis is a conditional PHO80(Ts) mutant indicated that neither PHO4 nor any other protein factor necessary for APase mRNA synthesis is transcriptionally regulated by PHO80 [7].
• Furthermore, high levels of PHO80 were shown to suppress the effect of a PHO85 deletion at a level close to full repression [22].
• Also, 10 independent single-amino-acid changes within PHO80 which resulted in the failure to repress PHO5 transcription were isolated [22].
• Our results suggest that Pho81 inhibits Pho80-Pho85 with a novel motif [18].

Other interactions of PHO80

• Thus, both the Pho80p-Pho85p kinase complex (by Pho4p phosphorylation) and a novel component of the N glycosylation pathway contribute to basal levels of aminoglycoside resistance in Saccharomyces cerevisiae [23].
• High-level expression of Pho80p results in aberrant PHO5 promoter regulation, characterized by failure to derepress in low-phosphate medium [24].
• This suggests that PHO81 may function by interacting with PHO80 or that these molecules compete for the same target [25].
• In addition, the chromosome contains two other phenotypic marker genes, HIS3 which is located distal from URA3, and PHO80 which is closely linked to the centromere [26].
• Importantly, we also show that Pho80-Pho85 and TORC1 converge on a single amino acid in Rim15 [6].

Analytical, diagnostic and therapeutic context of PHO80

• Using the affinity-purified antibodies in Western blotting experiments, the PHO85 protein was detected as a 36 kDa and the PHO80 protein as a 34 kDa protein [1].
• Sequence analysis shows that the vac5-1 allele encodes a truncated form of the Pho80 cyclin and overexpression of vac5-1 in pho80 delta cells causes a vacuole inheritance defect [11].

References