Transcriptional Regulation of CLN3 Expression by Glucose in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, the transition from the G(1) phase of the mitotic cycle into S phase is controlled by a set of G(1) cyclins that regulate the activity of the protein kinase encoded by CDC28. Yeast cells regulate progress through the G(1)/S boundary in response to nutrients, moving quickly through G(1) in glucose medium and more slowly in poorer medium. We have examined connections between glucose and the level of the message encoding Cln3, a G(1) cyclin. We found that glucose positively regulates CLN3 mRNA levels through a set of repeated AAGAAAAA (A(2)GA(5)) elements within the CLN3 promoter. Mutations in these sequences reduce both transcriptional activation and specific interaction between CLN3 promoter elements and proteins in yeast extracts. Creation of five point mutations, replacing the G’s within these repeats with T’s, in the CLN3 promoter substantially reduces CLN3 expression in glucose medium and inhibits the ability of the cells to maintain a constant size when shifted into glucose.