Identification and characterization of myo1 alleles affecting cytokinesis in Saccharomyces cerevisiae

Cytokinesis in the budding yeast Saccharomyces cerevisiae occurs via two coordinated pathways, the actomyosin contractile ring and the septum-formation process. The actomyosin contractile ring is not essential for viability in some strains. However, in at least one of those backgrounds, deletion of hof1, a gene important in septum formation, results in dependency on the contractile ring pathway for cytokinesis and viability (Vallen et al. 2000). A screen for mutants synthetically lethal with hof1 was utilized to identify genes required for the actomyosin pathway (Lippincott 2001). Complementation testing indicated that mutations in MYO1, a gene encoding the only type II myosin in budding yeast, and mutations in CYK3, a gene involved in the septum formation pathway of cytokinesis were isolated in the screen. Intriguingly, some mutants failed to complement both myo1 and cyk3. Meiotic segregation analysis and plasmid-linked suppression determined that most of these mutants carry myo1 alleles while one carries an allele of MLC1, a myosin light chain. Further characterization of the myo1 alleles may help define regions of Myo1p required for actomyosin ring assembly and contraction and elucidate mechanisms by which the actomyosin and septum formation pathways are coordinated