Project description:CENP-A, a variant of histone H3, is incorporated into centromeric chromatin and plays a role during kinetochore establishment. In fission yeast, the localization of CENP-A is limited to a region spanning 10 to 20 kb of the core domain of the centromere. Here, we report a mutant (rpt3-1) in which this region is expanded to 40 to 70 kb. Likely due to abnormal distribution of CENP-A, this mutant exhibits chromosome instability and enhanced gene silencing. Interestingly, the rpt3+ gene encodes a subunit of the 19S proteasome, which localizes to the nuclear membrane. While Rpt3 associates with centromeric chromatin, the mutant protein has lost this localization. A loss of the cut8+ gene encoding an anchor of the proteasome to the nuclear membrane causes similar phenotypes as observed in the rpt3-1 mutant. Thus, we propose that the proteasome (or its subcomplex) associates with centromeric chromatin and regulates distribution of CENP-A. Chromosomal distributions of differentially expressed centromere protein A in wild-type and a proteasome mutant.
Project description:CENP-A, a variant of histone H3, is incorporated into centromeric chromatin and plays a role during kinetochore establishment. In fission yeast, the localization of CENP-A is limited to a region spanning 10 to 20 kb of the core domain of the centromere. Here, we report a mutant (rpt3-1) in which this region is expanded to 40 to 70 kb. Likely due to abnormal distribution of CENP-A, this mutant exhibits chromosome instability and enhanced gene silencing. Interestingly, the rpt3+ gene encodes a subunit of the 19S proteasome, which localizes to the nuclear membrane. While Rpt3 associates with centromeric chromatin, the mutant protein has lost this localization. A loss of the cut8+ gene encoding an anchor of the proteasome to the nuclear membrane causes similar phenotypes as observed in the rpt3-1 mutant. Thus, we propose that the proteasome (or its subcomplex) associates with centromeric chromatin and regulates distribution of CENP-A.
Project description:CENP-A is a centromere-specific histone 3 variant essential for centromere specification. CENP-A partially replaces canonical histone H3 at the centromeres. How the particular CENP-A/H3 ratio at centromeres is precisely maintained is unknown. It also remains unclear how CENP-A is excluded from non-centromeric chromatin. Here we identify Ccp1, an uncharacterized NAP family protein in fission yeast that antagonizes CENP-A loading at both centromeric and non-centromeric regions. Like the CENP-A loading factor HJURP, Ccp1 interacts with CENP-A, and is recruited to centromeres at the end of mitosis in a Mis16-dependent manner. These data indicate that factors with opposing CENP-A loading activities are recruited to centromeres. Furthermore, Ccp1 also cooperates with H2A.Z to evict CENP-A assembled in euchromatin. Structural analyses indicate that Ccp1 forms a homodimer that is required for its anti-CENP-A loading activity. Our study establishes mechanisms for maintenance of CENP-A homeostasis at centromeres and the prevention of ectopic assembly of centromeres. Examination of cnp1 distribution in one wild type (wt) and two ccp1 mutants.