Meiotic Induction of the Yeast HOP1 Gene Is Controlled by Positive and Negative Regulatory Sites

Abstract

The process of meiosis and sporulation in the yeast Saccharomyces cerevisiae is a highly regulated developmental pathway dependent on genetic as well as nutritional signals. The HOP1 gene, which encodes a component of meiotic chromosomes, is not expressed in mitotically growing cells, but its transcription is induced shortly after yeast cells enter the meiotic pathway. Through a series of deletions and mutations in the HOP1 promoter, we located two regulatory sites that are essential for proper regulation of HOP1. One site, called URS1_H, brings about repression of HOP1 in mitotic cells and functions as an activator sequence in cells undergoing meiosis. The second site, which we designated UAS_H, acts as an activator sequence in meiotic cells and has similarity to the binding site of the mammalian CCAAT/enhancer binding protein (C/EBP). Both sites are required for full meiotic induction of the HOP1 promoter. We conclude that in mitotic yeast cells, the URS1_h site maintains the repressed state of the HOP1 promoter, masking the effect of the UAS_H site. Upon entry into meiosis, repression is lifted, allowing the URS1_H and UAS_H sites to activate high-level transcription.