A DNA polymerase α accessory protein, Mcl1, is required for propagation of centromere structures in fission yeast

Specialized chromatin exists at centromeres and must be precisely transmitted during DNA replication. The mechanisms involved in the propagation of these structures remain elusive. Fission yeast centromeres are composed of two chromatin domains: the central CENP-A^cnp1 kinetochore domain and flanking heterochromatin doamins. Here we show that fission yeast Mcl1, a DNA polymerase α (Polα) accessory protein, is critical maintenance of centromeric chromatin. In a screen for mutants that alleviate both central domain and outer repeat silencing, we isolated several cos mutants, of which cos1 is allelic to mcl1. The mcl1-101 mutation causes reduced CENP-A^cnp1 in the central domain and aberrant increase in histone acetylation in both domains. These phenotypes are also observed in a mutant of swiZ⁺, which encodes catalytic subunit of Polα. Mcl1 forms S-phase-specific nuclear foci, which colocalize which those of PCNA and Polα. These results suggest that Mcl1 and Polα are required for propagation of centromere chromatin structures during DNA replication.