IDENTIFICATION AND CLONING OF THE CHL4 GENE CONTROLLING CHROMOSOME SEGREGATION IN YEAST

A collection of chl mutants characterized by decreased fidelity of chr omosome transmission and by minichromosome nondisjunction in mitosis w as examined for the ability to maintain nonessential dicentric plasmid s. In one of the seven mutants analyzed, chl4, dicentric plasmids did not depress cell division. Moreover, nonessential dicentric plasmids w ere maintained stably without any rearrangements during many generatio ns in the chl4 mutant. The rate of mitotic heteroallelic recombination in the chl4 mutant was not increased compared to that in an isogenic wild-type strain. Analysis of the segregation of a marked chromosome i ndicated that sister chromatid nondisjunction and sister chromatid los s contributed equally to chromosome malsegregation in the chl4 mutant. A genomic clone of CHL4 was isolated by complementation of the chl4-1 mutation and was physically mapped to the right arm of chromosome IV near the SUP2 gene. Nucleotide sequence analysis of CHL4 clone reveale d a 1.4-kb open reading frame coding for a 53-kD predicted protein whi ch does not have homology to published proteins. A strain containing a null allele of CHL4 is viable under standard growth conditions but ha s a temperature-sensitive phenotype (conditional lethality at 36-degre es). We suggest that the CHL4 gene is required for kinetochore functio n in the yeast Saccharomyces cerevisiae.