CENTROMERES, CHECKPOINTS AND CHROMATID COHESION

An emerging view is that the formation of active centromeres is modula ted in an epigenetic manner reflecting the association of centromeres with heterochromatin. Support for this comes from studies on fission y east centromeres, the properties of human neocentromeres and dicentric chromosomes, and analyses of Drosophila minichromosome deletion deriv atives. A link has been established between tension across kinetochore s and the phosphorylation status of kinetochore components. Vertebrate homologues of yeast MAD2 have recently been isolated and localized to kinetochores, indicating that components of the spindle integrity che ckpoint are conserved. The linkage between sister chromatids is only d issolved at anaphase during mitotic and meiotic divisions. Phenotypic and localization data combined with their pattern of rapid degradation at anaphase have implicated several yeast and Drosophila proteins in aspects of sister chromatid cohesion.