RESUMEN
The mitotic kinetochore forms at the centromere for proper chromosome segregation. Deposition of the centromere-specific histone H3 variant, spCENP-A/Cnp1, is vital for the formation of centromere-specific chromatin and the Mis17-Mis6 complex of the fission yeast Schizosaccharomyces pombe is required for this deposition. Here we identified extragenic suppressors for a Mis17-Mis6 complex temperature-sensitive (ts) mutant, mis17-S353P, using whole-genome sequencing. The large and small daughter nuclei phenotype observed in mis17-S353P was greatly rescued by these suppressors. Suppressor mutations in two ribonuclease genes involved in the mRNA decay pathway, exo2 and pan2, may affect Mis17 protein level, as mis17 mutant protein level was recovered in mis17-S353P exo2 double mutant cells. Suppressor mutations in EKC/KEOPS complex genes may not regulate Mis17 protein level, but restored centromeric localization of spCENP-A/Cnp1, Mis6 and Mis15 in mis17-S353P Therefore, the EKC/KEOPS complex may inhibit Mis17-Mis6 complex formation or centromeric localization. Mutational analysis in protein structure indicated that suppressor mutations in the EKC/KEOPS complex may interfere with its kinase activity or complex formation. Our results suggest that the mRNA decay pathway and the EKC/KEOPS complex negatively regulate Mis17-Mis6 complex-mediated centromere formation by distinct and unexpected mechanisms.
Asunto(s)
Proteínas de Ciclo Celular/metabolismo , Centrómero/genética , Centrómero/metabolismo , Estabilidad del ARN , Proteínas de Schizosaccharomyces pombe/metabolismo , Schizosaccharomyces/genética , Schizosaccharomyces/metabolismo , Regulación Fúngica de la Expresión Génica , Genes Reporteros , Complejos Multiproteicos/metabolismo , Mutación , FenotipoRESUMEN
Eukaryotic chromosome segregation requires a protein complex known as the kinetochore that mediates attachment between mitotic spindle microtubules and centromere-specific nucleosomes composed of the widely conserved histone variant CENP-A. Mutations in kinetochore proteins of the fission yeast Schizosaccharomyces pombe lead to chromosome missegregation such that daughter cells emerge from mitosis with unequal DNA content. We find that multiple copies of Msc1-a fission yeast homolog of the KDM5 family of proteins-suppresses the temperature-sensitive growth defect of several kinetochore mutants, including mis16 and mis18, as well as mis6, mis15, and mis17, components of the Constitutive Centromere Associated Network (CCAN). On the other hand, deletion of msc1 exacerbates both the growth defect and chromosome missegregation phenotype of each of these mutants. The C-terminal PHD domains of Msc1, previously shown to associate with a histone deacetylase activity, are necessary for Msc1 function when kinetochore mutants are compromised. We also demonstrate that, in the absence of Msc1, the frequency of localization to the kinetochore of Mis16 and Mis15 is altered from wild-type cells. As we show here for msc1, others have shown that elevating cnp1 levels acts similarly to promote survival of the CCAN mutants. The rescue of mis15 and mis17 by cnp1 is, however, independent of msc1 Thus, Msc1 appears to contribute to the chromatin environment at the centromere: the absence of Msc1 sensitizes cells to perturbations in kinetochore function, while elevating Msc1 overcomes loss of function of critical components of the kinetochore and centromere.
Asunto(s)
Cromatina/genética , Proteínas de Unión al ADN/metabolismo , Cinetocoros/metabolismo , Proteínas de Schizosaccharomyces pombe/metabolismo , Schizosaccharomyces/genética , Proteínas Portadoras/genética , Proteínas Portadoras/metabolismo , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Centrómero/genética , Centrómero/metabolismo , Cromatina/metabolismo , Ensamble y Desensamble de Cromatina , Proteínas Cromosómicas no Histona/genética , Proteínas Cromosómicas no Histona/metabolismo , Segregación Cromosómica , Proteínas de Unión al ADN/química , Proteínas de Unión al ADN/genética , Dominios Proteicos , Proteínas de Schizosaccharomyces pombe/química , Proteínas de Schizosaccharomyces pombe/genéticaRESUMEN
The late Middle Pleistocene cave site of Pinnacle Point 13B (PP13B, South Africa) has provided the archaeologically oldest evidences yet known of human consumption of marine resources. Among the marine invertebrates recognised at PP13B, an isolated whale barnacle compartment was tentatively determined as Coronula diadema and regarded as indirect evidence of human consumption of a baleen whale (likely Megaptera novaeangliae). In this paper we redetermine this coronulid specimen as Cetopirus complanatus. This record significantly extends the fossil history of C. complanatus back by about 150 ky, thus partially bridging the occurrence of Cetopirus fragilis in the early Pleistocene to the latest Quaternary record of C. complanatus. Since C. complanatus is currently known as a highly specific phoront of right whales (Eubalaena spp.), we propose that the late Middle Pleistocene human groups that inhabited PP13B fed on a stranded southern right whale. Therefore, the whale barnacle from PP13B suggests the persistence of a southern right whale population off South Africa during the predominantly glacial MIS 6, thus evoking the continuity of cetacean migrations and antitropical distribution during that global cold phase. Interestingly, the most ancient evidence of humans feeding on a whale involves Eubalaena, historically the most exploited cetacean genus, and currently still seriously threatened with extinction due to human impact.