SACCHAROMYCES-CEREVISIAE KINESIN-RELATED AND DYNEIN-RELATED PROTEINS REQUIRED FOR ANAPHASE CHROMOSOME SEGREGATION

The Saccharomyces cerevisiae kinesin-related gene products Cin8p and K ip1p function to assemble the bipolar mitotic spindle. The cytoplasmic dynein heavy chain homologue Dyn1p (also known as Dhc1p) participates in proper cellular positioning of the spindle. In this study, the rel ies of these motor proteins in anaphase chromosome segregation were ex amined. While no single motor was essential, loss of function of all t hree completely halted anaphase chromatin separation. As combined moto r activity was diminished by mutation, both the velocity and extent of chromatin movement were reduced, suggesting a direct role for all thr ee motors in generating a chromosome-separating force. Redundancy for function between different types of microtubule-based motor proteins w as also indicated by the observation that cin8 dyn1 double-deletion mu tants are inviable. Our findings indicate that the bulk of anaphase ch romosome segregation in S. cerevisiae is accomplished by the combined actions of these three motors.