New mechanisms regulating gene PHO3 and PHO5 expression in yeast Saccharomyces cerevisiae depending on medium composition.
Vladimir A. Savinov (1), Anastasia Y. Fizikova (2), Elena V. Sambuk (3)
(1) St.-Petersburg, 192283, Budapeshtskaya st., 91-1, 129, Russia; (2) St.-Petersburg, 197373, pr. Aviakonstructorov, 44-2, 120, Russia; (3) St.-Petersburg, 195112, Novocherkassky pr., 26, 117, Russia
An expression of yeast genes is regulated according to changes of environmental conditions, generally carbon, nitrogen and phosphate concentrations being essential medium components. Isozymes' presence provides cell with extensive possibilities for adaptation. Genes PHO5 and PHO3 of yeast encode structures of acid phosphatase isozymes that provide utilization of various phosphate compounds and which activity depends on exogenous phosphate and thiamin quantities, respectively. PHO5 gene encodes the phosphate-regulated acid phosphatase expressed at low level of intracellular phosphate. PHO3 gene encodes the constitutive, but thiamin-repressible acid phosphatase that plays a role in the hydrolysis of thiamin phosphates and does not depend on phosphate concentrations. These two genes are the result of a tandem duplication, but have partly divergent promoter sequences that may explain their different regulation. In this study we examine the abilities of phosphate, nitrogen and carbon metabolisms' regulators to affect transcription degree of genes PHO3 and PHO5. We proved that PHO3 and PHO5 promoters' activity depended on nitrogen source quality in medium and propose the GATA-activator of nitrogen-regulated genes Gln3p to bind GATAA sites of PHO3 promoter and function as a repressor in cells growing with poor nitrogen source, urea. In addition, some phosphate metabolism's regulators (Pho85p) are known to be involved in utilization of different carbon sources.