STRUCTURE-FUNCTION-RELATIONSHIPS OF THE YEAST CYCLIN-DEPENDENT KINASEPHO85

The PHO85 gene of Saccharomyces cerevisiae encodes a cyclin-dependent kinase involved in both transcriptional regulation and cell cycle prog ression. Although a great deal is known concerning the structure, func tion, and regulation of the highly homologous Cdc28 protein kinase, li ttle is known concerning these relationships in regard to Pho85. In th is study, we constructed a series of Pho85-Cdc28 chimeras to map the r egion(s) of the Pho85 molecule that is critical for function of Pho85 in repression of acid phosphatase (PHO5) expression. Using a combinati on of site-directed and ethyl methanesulfonate-induced mutagenesis, we have identified numerous residues critical for either activation of t he Pho85 kinase, interaction of Pho85 with the cyclin-like molecule Ph o80, or substrate recognition. Finally, analysis of mutations analogou s to those previously identified in either Cdc28 or cdc2 of Schizosacc haromyces pombe suggested that the inhibition of Pho85-Pho80 activity is mechanistically different from that seen in the other cyclin-depend ent kinases.