Sim4: a novel fission yeast kinetochore protein required for centromeric silencing and chromosome segregation.
Fission yeast centromeres are composed of two domains: the central core and the outer repeats. Although both regions are required for full centromere function, the central core has a distinct chromatin structure and is likely to underlie the kinetochore itself, as it is associated with centromere-specific proteins. Genes placed within either region are transcriptionally silenced, reflecting the formation of a functional kinetochore complex and flanking centromeric heterochromatin. Here, transcriptional silencing was exploited to identify components involved in central core silencing and kinetochore assembly or structure. The resulting sim (silencing in the middle of the centromere) mutants display severe chromosome segregation defects. sim2+ encodes a known kinetochore protein, the centromere-specific histone H3 variant Cnp1CENP-A. sim4+ encodes a novel essential coiled-coil protein, which is specifically associated with the central core region and is required for the unusual chromatin structure of this region. Sim4 coimmunoprecipitates with the central core component Mis6 and, like Mis6, affects Cnp1CENP-A association with the central domain. Functional Mis6 is required for Sim4 localization at the kinetochore. Our analyses illustrate the fundamental link between silencing, chromatin structure, and kinetochore function, and establish defective silencing as a powerful approach for identifying proteins required to build a functional kinetochore.
Wellcome Trust Centre for Cell Biology, Institute of Cell and Molecular Biology, 6.34 Swann Building, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JR, UK. robin.allshire@ed.ac.uk
Alison L
AL
Pidoux
William
W
Richardson
Robin C
RC
Allshire
D000595:Amino Acid Sequence / Q000235:genetics; D001483:Base Sequence / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002455:Cell Division / Q000235:genetics; D002503:Centromere / Q000235:genetics* / Q000378:metabolism; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics* / Q000302:isolation & purification* / Q000378:metabolism; D020090:Chromosome Segregation / Q000235:genetics*; D015966:Gene Expression Regulation, Fungal / Q000235:genetics; D020868:Gene Silencing / Q000502:physiology*; D005820:Genetic Testing; D018386:Kinetochores / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D012568:Schizosaccharomyces / Q000166:cytology / Q000235:genetics* / Q000378:metabolism; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics* / Q000302:isolation & purification* / Q000378:metabolism; D037941:Silencer Elements, Transcriptional / Q000235:genetics
D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; C410349:Cnp1 protein, S pombe; C107314:Mis6 protein, S pombe; D029702:Schizosaccharomyces pombe Proteins