Presidential Faculty Fellow

O’shea酵母的生长是由营养物质的供应来维持的。磷酸盐是必需的营养物。当磷酸盐受到限制时，酸性磷酸酶就会发生转录。分泌的这种酶能水解有机分子的磷酸基，产生磷酸离子。PHO5基因编码磷酸酶；酵母在含有Pi的培养基中生长时，转录受到严格抑制。已鉴定出该基因的三个正调控因子和两个负调控因子。两种正调节因子已被证明是与启动子结合的转录调节因子。这两个负调节器都是必不可少的；任何一个缺失都会导致高水平的基因表达。其中一种是PHO80，与酵母菌周期蛋白同源（它调节细胞分裂）。另一个负调节因子PHO85是一种与CDC相关的蛋白激酶。负调节复合体只有在酵母生长在高磷酸盐环境时才能磷酸化转录因子PHO4。这种磷酸化与基因抑制有关。在低Pi条件下的生长导致其中一种正调节因子PHO81抑制激酶复合物。激酶活性的降低与基因的抑制有关；这是由PHO4的作用辅助的，PHO4的生化活性尚未被表征。酵母需要磷酸盐来生长和繁殖。当磷酸盐含量低时，酵母分泌一种特殊的酶来分解含有磷酸盐的有机化合物，以更新供应。研究人员发现，调节这种特殊酶产生的分子也调节细胞分裂。这是适应环境的一个显著例子。使用相同或类似的分子来控制磷酸盐的使用，这是生长和分裂所必需的，也指导细胞自我繁殖。＊＊＊

9553140 O'Shea Yeast growth is sustained by the availability of nutrients. Phosphate is a required nutrient. When phosphate is limiting transcription of an acid phosphatase occurs. This enzyme which is secreted hydrolyzes phosphoryl groups of organic molecules to yield phosphate ion. The PHO5 gene encodes the phosphatase; transcription is tightly repressed when yeast are grown in medium containing Pi. Three positive regulators and two negative regulators of the gene have been identified. Two of the positive regulators have been shown to be transcriptional regulators that bind to the promoter. Both of the negative regulators are essential; deletion of either results in high levels of gene expression. One of these, PHO80, is homologous to a yeast cyclin (which regulates cell division). The other negative regulator, PHO85, is a CDC related protein kinase. The complex of negative regulators phosphorylates transcription factor PHO4 only when yeast are grown in high phosphate. This phosphorylation is correlated with gene repression. Growth in low Pi results in one of the positive regulators, PHO81, inhibiting the kinase complex. The reduced activity of the kinase is correlated with derepression of the gene; this is assisted by the action of PHO4 whose biochemical activity is not characterized. %%% Yeast require phosphate to grow and multiply. When phosphate amounts are low the yeast secrete a special enzyme that breaks down organic compounds that contain phosphate to renew the supplies. The investigator has found that the same molecules that regulate the production of the special enzyme also regulate cell division. This is a remarkable example of adaptation to the environment. The use of the same or similar molecules that control phosphate use which is necessary for growth and division also direct the cell to reproduce itself. ***