Chromatin and Transcriptional Regulation of CHA1 in Yeast

Health Research Incorporated/New York State Department Of Health, Menands NY

Investigators

Abstract

The long term goal of this project is to gain new understanding into mechanisms of chromatin-mediated gene regulation. DNA in higher organisms, including humans, is packaged into nucleosomes by wrapping around an octamer of histone proteins. This creates a potential impediment to protein-DNA interactions needed for transcription of DNA into RNA, and so at many genes these nucleosomes must be remodeled to allow transcription to occur. Enzymes and pathways that allow chromatin remodeling have been identified for some genes, but for many others these pathways remain unknown. To gain new insight into regulation of transcription by chromatin, this work will focus on the Saccharomyces cerevisiae CHA1 gene. The CHA1 promoter is readily inducible by addition of serine to growth medium, and its chromatin is remodeled upon activation. Genetic and biochemical approaches will be used to ascertain the mechanism by which CHA1 chromatin structure is remodeled during activation. Repression of CHA1 in the absence of inducing signal will also be investigated. It was shown that loss of the histone H3 amino terminus causes strong CHA1 transcription under uninduced conditions, accompanied by chromatin remodeling. Novel histone H3 mutations that cause CHA1 derepression have been isolated, and will be used in a suppressor screen to uncover genes contributing to histone-mediated CHA1 repression. The significance of this work lies in its investigation of basic mechanisms of chromatin-mediated gene regulation. Chromatin has been implicated in gene regulation in development and in hormone regulation, and so is of fundamental importance. Since remodeling of the CHA1 gene does not use known mechanisms of chromatin remodeling, these studies are expected to yield fundamental new insight into this aspect of gene regulation. Furthermore, since the proteins involved in gene regulation and in chromatin are highly conserved between yeast and higher eukaryotes, including humans, these studies will reveal aspects of regulation that are likely to be common across the eukaryotic kingdom.