CSE1 AND CSE2, 2 NEW GENES REQUIRED FOR ACCURATE MITOTIC CHROMOSOME SEGREGATION IN SACCHAROMYCES-CEREVISIAE

By monitoring the mitotic transmission of a marked chromosome bearing a defective centromere, we have identified conditional alleles of two genes involved in chromosome segregation (cse). Mutations in CSE1 and CSE2 have a greater effect on the segregation of chromosomes carrying mutant centromeres than on the segregation of chromosomes with wild-ty pe centromeres. In addition, the cse mutations cause predominantly non disjunction rather than loss events but do not cause a detectable incr ease in mitotic recombination. At the restrictive temperature, cse1 an d cse2 mutants accumulate large-budded cells, with a significant fract ion exhibiting aberrant binucleate morphologies. We cloned the CSE1 an d CSE2 genes by complementation of the cold-sensitive phenotypes. Phys ical and genetic mapping data indicate that CSE1 is linked to HAP2 on the left arm of chromosome VII and CSE2 is adjacent to PRP2 on chromos ome XIV. CSE1 is essential and encodes a novel 109-kDa protein. CSE2 e ncodes a 17-kDa protein with a putative basic-region leucine zipper mo tif. Disruption of CSE2 causes chromosome missegregation, conditional lethality, and slow growth at the permissive temperature.