A suppressor of a centromere DNA mutation encodes a putative protein kinase (MCK1)

A new approach to identify genes involved in Saccharomyces cerevisiae kinetochore function is discussed. A genetic screen was designed to recover extragenic dosage suppressors of a CEN DNA mutation. This method identified two suppressors, designated MCK1 and CMS2. Increased dosage of MCK1 specifically suppressed two similar CEN DNA mutations in CDEIII, but not comparably defective CEN DNA mutations in CDEI or CDEII. A strain containing a null allele of MCK1 was viable under standard growth conditions, had a cold-sensitive phenotype (conditional lethality at 11 degrees C), and grew slowly on Benomyl (a microtubule-destabilizing drug). Furthermore, when grown at 18 degrees C or in the presence of Benomyl, the null mutant exhibited a dramatic increase in the rate of mitotic chromosome loss. The allele-specific suppression and chromosome instability phenotypes suggest that MCK1 plays a role in mitotic chromosome segregation specific to CDEIII function. The MCK1 gene encodes a putative protein-serine/threonine kinase, which suggests a possible role for the MCK1 protein in regulating the activity of centromere-binding proteins by phosphorylation. MCK1 was identified and cloned independently for its involvement in the induction of meiosis and is identical to a gene that encodes a phosphotyrosyl protein with protein kinase activity.