CENTROMERE POSITION IN BUDDING YEAST - EVIDENCE FOR ANAPHASE-A

Although general features of chromosome movement during the cell cycle are conserved among all eukaryotic cells, particular aspects vary bet ween organisms. Understanding the basis for these variations should pr ovide significant insight into the mechanism of chromosome movement. I n this context, establishing the types of chromosome movement in the b udding yeast Saccharomyces cerevisiae is important since the complexes that mediate chromosome movement (microtubule organizing centers, spi ndles, and kinetochores) appear much simpler in this organism than in many other eukaryotic cells. We have used fluorescence in situ hybridi zation to begin an analysis of chromosome movement in budding yeast. O ur results demonstrate that the position of yeast centromeres changes as a function of the cell cycle in a manner similar to other eukaryote s. Centromeres are skewed to the side of the nucleus containing the sp indle pole in G1; away from the poles in mid-M and clustered near the poles in anaphase and telophase. The change in position of the centrom eres relative to the spindle poles supports the existence of anaphase A in budding yeast. In addition, an anaphase A-like activity independe nt of anaphase B was demonstrated by following the change in centromer e position in telophase-arrested cells upon depolymerization and subse quent repolymerization of microtubules. The roles of anaphase A activi ty and G1 centromere positioning in the segregation of budding yeast c hromosomes are discussed. The fluorescence in situ hybridization metho dology and experimental strategies described in this study provide pow erful new tools to analyze mutants defective in specific kinesin-like molecules, spindle components, and centromere factors, thereby elucida ting the mechanism of chromosome movement.