Ste12 and Mcm1 Regulate Cell Cycle-Dependent Transcription of FAR1

Abstract

The transcripts of many genes involved in Saccharomyces cerevisiae mating were found to fluctuate during the cell cycle. In the absence of a functional Ste12 transcription factor, both the levels and the cell cycle pattern of expression of these genes were affected. FUS1 and AGA1 levels, which are maximally expressed only in G₁-phase cells, were strongly reduced in ste12⁻ cells. The cell cycle transcription pattern for FAR1 was changed in ste12⁻ cells: the gene was still significantly expressed in G₂/M, but transcript levels were strongly reduced in G₁ phase, resulting in a lack of Farl protein accumulation. G₂/M transcription of FAR1 was dependent on the transcription factor Mcm1, and expression of a gene with Mcml fused to a strong transcriptional activation domain resulted in increased levels of FAR1 transcription. The pattern of cell cycle-regulated transcription of FAR1 could involve combinatorial control by Ste12 and Mcml. Forced G₁ expression of FAR1 from the GAL1 promoter restored the ability to arrest in response to pheromone in ste12⁻ cells. This indicates that transcription of FAR1 in the G₁ phase is essential for accumulation of the protein and for pheromone-induced cell cycle arrest.