The fission yeast chrome domain encoding gene chp1+ is required for chromosome segregation and shows a genetic interaction with alpha-tubulin

In eukaryotes, the segregation of chromosomes is co-ordinated by the centromere and must proceed accurately if aneuploidy and cell death are to be avoided. The fission yeast centromere is complex, containing highly repetitive regions of DNA showing the Characteristics of heterochromatin. Two proteins, Swi6p and Clr4p, that are associated with the fission yeast centromere also contain a chrome (chromatin organisation modifier) domain and are required for centromere function. We have analysed a novel fission yeast gene encoding a putative chrome domain called chp1(+) (chromo domain protein in Schizosaccharomyces pombe). In the absence of Chp1p protein, cells are viable but show chromosome segregation defects such as lagging chromosomes an the spindle during anaphase and high rates of minichromosome loss, phenotypes which are also displayed by swi6 and clr4. A fusion protein between green fluorescent protein (GFP) and Chp1p, like Swi6p, is localized to discrete sites within the nucleus. In contrast to Swi6p and Clr4p, Chp1p is not required to repress silent mating-type genes. We demonstrate a genetic interaction between chp1(+) and alpha-tubulin (nda2(+)) and between swi6(+) and beta-tubulin (nda3(+)). Chp1p and Swi6p proteins may be components of the kinetochore which captures and stabilizes the microtubules of the spindle.