Distinct protein interaction domains and protein spreading in a complex centromere.

Fission yeast (Schizosaccharomyces pombe) centromeres are composed of large (40-100 kb) inverted repeats that display heterochromatic features, thus providing a good model for higher eukaryotic centromeres. The association of three proteins that mediate region-specific silencing across centromere 1 has been mapped by quantitative chromatin immunoprecipitation. Swi6 and Chp1 are confined to the flanking outer repeats and Swi6 can spread across at least 3 kb of extraneous chromatin in cen1. In contrast, Mis6 coats the inner repeats and central core. tRNA genes demarcate this transition zone. These analyses clearly define two distinct domains within this complex centromere which interact with different proteins.