Regulation of yeast chromosome segregation by Ipl1 protein kinase and type 1 protein phosphatase.

Chromosome segregation is a complicated process that involves the coordinated functioning of a large number of cellular components. In this process, many proteins are activated and inactivated in a strict temporal order. While much progress has been made recently in the identification of structural components that are involved in chromosome segregation, relatively little is known about their regulation. We have investigated the chromosome segregation process in the budding yeast Saccharomyces cerevisiae. Our results indicate that this process absolutely requires a functional Ipl1 protein kinase. Upon inactivation of this protein kinase, yeast cells missegregate chromosomes severely and die within a single cell cycle. Furthermore, the inviability caused by a partial reduction in Ipl1 function can be rescued by perturbations that reduce type 1 protein phosphatase activity, thus suggesting that type 1 protein phosphatase acts in opposition to the Ipl1 protein kinase to insure the high fidelity of chromosome segregation in yeast cells. The purpose of this article is to describe some of our ongoing efforts to characterize Ipl1 and PP1 functions.