Yeast Genetics and Molecular Biology 1998
College Park, Maryland
August 1998

Name: McBride, Helen
Mailing Address: Dept. of Oncological Sciences, University of Utah, 50 N. Medical Drive, Salt Lake City, UT 84132, US
Email Address: helen.mcbride@genetics.utah.edu
Phone and Fax numbers: 1-801-581-3607, 1-801-581-3607

034

The Pho85 Cyclin Dependent Kinase Regulates Ash1 Protein Daughter Cell Localization in Saccharomyces cerevisiae.


Helen McBride (1) , Anita Sil (2), Vivien Measday (3), Jason Moffat (3), Mary Maxon (2), Michael Costanza (3), Ira Herskowitz (2), Brenda Andrews (3), David Stillman (1)
(1) Dept. of Oncological Sciences, University of Utah, 50 N. Medical Drive, Salt Lake City, UT 84132, US; (2) University of California San Francisco, Department of Biochemistry and Biophysics, San Francisco, California, 94143 USA; (3) University of Toronto, Department of Medical Genetics and Microbiology, Toronto, Ontario, M5S1A8 Canada

The Ash1 protein is a daughter-specific negative regulator of HO expression in S. cerevisiae . The mRNA and the protein are localized to the daughter cell at the end of mitosis, repressing HO expression in daughter cells. PHO85 encodes a cyclin dependent kinase involved in cell cycle progression and control of phosphate and glycogen metabolism. A pho85 mutation reduces HO expression and consequently also reduces mating type switching in mother cells. This decrease in HO expression is likely mediated by Ash1, as Ash1 protein inappropriately accumulates in mother cells in a pho85 mutant as judged by indirect immunofluorescence. A pho85 ash1 double mutant expresses HO , indicating that Ash1 is responsible for the reduced HO expression in a pho85 mutant. Neither the timing nor the abundance of Ash1 mRNA is altered in a pho85 mutant, and the Ash1 mRNA accumulates properly in daughter cells, suggesting that PHO85 may regulate Ash1 protein stability rather than message accumulation. This result separates PHO85 from the SHE genes, some of which are structural proteins involved in the localization of Ash1 mRNA. We show that Ash1 is an in vitro substrate for the Pho85 Cdk, and models for the regulation of Ash1 protein accumulation are presented.

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