The Kar3-interacting protein Cik1p plays a critical role in passage through meiosis I in Saccharomyces cerevisiae.

Meiosis I in Saccharomyces cerevisiae is dependent upon the motor protein Kar3. Absence of Kar3p in meiosis results in an arrest in prophase I. Cik1p and Vik1p are kinesin-associated proteins known to modulate the function of Kar3p in the microtubule-dependent processes of karyogamy and mitosis. Experiments were performed to determine whether Cik1p and Vik1p are also important for the function of Kar3p during meiosis. The meiotic phenotypes of a cik1 mutant were found to be similar to those of kar3 mutants. Cells without Cik1p exhibit a meiotic defect in homologous recombination and synaptonemal complex formation. Most cik1 mutant cells, like kar3 mutants, arrest in meiotic prophase; however, in cik1 mutants this arrest is less severe. These data are consistent with the model that Cik1p is necessary for some, but not all, of the roles of Kar3p in meiosis I. vik1 mutants sporulate at wild-type levels, but have reduced spore viability. This loss in viability is partially attributable to vegetative chromosome loss in vik1 diploids. Cellular localization experiments reveal that Kar3p, Cik1p, and Vik1p are present throughout meiosis and are consistent with Cik1p and Vik1p having different meiotic roles.