Centromeric Chromatin and Chromosome Segregation In Saccharomyces Cerevisiae

University Of Arkansas, Fayetteville AR

Investigators

Abstract

The faithful transmission of chromosomes during cell division is essential for the well-being of an organism and the maintenance of the species. During cell division a complex set of structures work in concert to ensure the accurate transmission of chromosomes to daughter cells. A key structural component in this process is the centromere, the specialized DNA region within each chromosome where a complex of proteins, the kinetochore, assembles to attach the chromosome to the mitotic spindle. Many studies have provided evidence that chromatin structure is critical in maintaining the fidelity of chromosome transmission, but its roles are not understood. The long-term goal of this project is to understand how chromatin structure affects chromosome segregation, in particular the role that histones, the protein components of the nucleosome, have in this process. This study uses the yeast Saccharomyces cerevisiae as a eukaryotic model organism. The simple gene organization in S. cerevisiae, the ease of genetic manipulations, and the strong evolutionary conservation of the histone proteins and nucleosome structure make this yeast an excellent model system to study histone function. Current evidence indicates that histone H2A, one of the four histones that form the core of chromatin, is essential for normal centromere function. This project aims to identify factors that interact with histone H2A in the formation of a functional centromere-kinetohore complex, using genetic and biochemical approaches. The first major goal is to isolate and identify factors that suppress the increase-in-ploidy defect caused by a mutant histone H2A. Previous work showed that the ploidy increase caused by the H2A mutant is associated with defects in chromosome segregation and an altered centromeric chromatin structure. Thus, suppressors of the ploidy increase will provide important information about the components required for the formation of centromeric chromatin and their interactions with kinetochore proteins. The second major goal is to characterize two previously isolated suppressors of the increase-in-ploidy defect of the H2A mutant. These suppressors, PLO1 and PLO2, encode two new and uncharacterized proteins with significant homology to each other, and both proteins share limited sequence similarity to the mammalian centromere-binding proteins CENP-E and CENP-F, respectively. The characterization of PLO1 and PLO2 will determine the relevance of this homology with respect to their function. Preliminary work indicates that PLO1 is involved in some aspect of chromosome segregation. These studies will advance our knowledge of the factors that interact with histones and kinetochore proteins at the centromere, and will help to elucidate the mechanisms by which centromeric chromatin controls chromosome segregation. Ultimately, this work will provide insight into a basic cellular process essential to maintain the integrity of an organism's genetic information.