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.