Simultaneous expression of both MAT loci in haploid cells suppresses mutations in yeast microtubule motor genes

The kinesin-related Cin8p and cytoplasmic dynein are microtubule-associated motor proteins required for anaphase spindle elongation in the yeast Sacch aromyces cerevisiae. Cells deleted for DYN1 (the gene encoding the dynein h eavy chain) and carrying the temperature-sensitive allele cin8-3 cannot gro w at temperatures above 35 degreesC. Here, we report that the temperature s ensitivity of haploid cin8-3 dyn1 Delta cells is suppressed by the simultan eous presence of the loci MATa and MAT alpha, which contain the regulatory genes that determine mating-type and ploidy-dependent phenotypes. The prese nce of the two MAT loci also rendered haploid cells more resistant to the a ntimicrotubule drug benomyl. Our results suggest that, in preparation for h andling double the amount of DNA in mitosis, properties of microtubules in diploid cells are modified in a pathway controlled by the mating-type regul atory genes.