CLONING OF THE STE5 GENE OF SACCHAROMYCES-CEREVISIAE AS A SUPPRESSOR OF THE MATING DEFECT OF CDC25 TEMPERATURE-SENSITIVE MUTANTS

The STE5 gene of Saccharomyces cerevisiae was cloned using a screening procedure designed to isolate genes of the S. cerevisiae pheromone re sponse pathway. We screened a yeast genomic high-copy-number plasmid l ibrary for genes that allow mating of cdc25ts mutants at the restricti ve temperature without affecting the cell-cycle-arrest phenotype. One of the genes cloned was identified by genetic analysis as STE5. STE5 e ncodes a predicted open reading frame of 916 amino acids and exhibits significant homology to Far1 protein. RNA blot analysis reveals that S TE5 gene transcription is regulated by the mating type of the cell and depends on an intact pheromone-response pathway.