Cell cycle dependent methylation of Dam1 contributes to kinetochore integrity and faithful chromosome segregation.

Abstract

The kinetochore, a megadalton structure composed of centromeric (CEN) DNA and protein complexes, is required for faithful chromosome segregation in eukaryotes. The evolutionarily conserved Dam1/DASH complex (Ska1 in metazoans) is one of the essential protein sub-complexes of the budding yeast kinetochore. Previous studies showed that methylation of lysine residue 233 in Dam1 by Set1 is important for haploid growth as mutation of lysine 233 to alanine results in lethality. In this study, we report that Set1-mediated cell cycle dependent Dam1 lysine methylation contributes to kinetochore assembly and chromosomal stability. Our results show that Dam1 methylation is cell cycle regulated with the highest levels of methylation in metaphase. Consistent with these results, co-immunoprecipitation experiments revealed an interaction between Dam1 with Set1 in metaphase cells. Set1 has been shown to colocalize with Jhd2, a histone lysine demethylase which demethylates Set1-methylated histones. Affinity purification-based mass spectroscopy of Jhd2 associated proteins identified seven of the ten subunits of the Dam1 complex; an association of Jhd2 with non-histone proteins, such as Dam1 has not been previously reported. We confirmed the interaction of Jhd2 with Dam1 and showed that cells overexpressing JHD2 exhibit reduced levels of methylated lysine in Dam1 in wild type and UBP8 deletion strains, growth defects in kinetochore mutants, reduced levels of kinetochore proteins at CEN chromatin, defects in kinetochore biorientation and chromosome missegregation. In summary, we have shown that cell cycle dependent methylation of Dam1 plays a crucial role in the maintenance of kinetochore assembly for faithful chromosome segregation.