Sororin, the cell cycle and sister chromatid cohesion

Sister chromatid cohesion is essential for the maintenance of genome integrity. Errors in regulation of cohesion result in increased sensitivity to DNA damage, mis-segregation of chromosomes, and loss of genetic information. We recently showed that sororin is an essential regulator of sister chromatid cohesion in vertebrates. Interestingly, we identified sororin in a screen for proteins whose levels are controlled by the Anaphase Promoting Complex (APC), a cell cycle-regulated ubiquitin ligase. Ubiquitination by the APC and the resulting degradation ensure that sororin levels are low throughout G(1) and only rise during S phase. We speculate that this regulation is an essential part of the mechanism that ensures that cohesion is established only after there are in fact two sister chromatids to tie together. Cohesion thus established can then be used both to mediate recombinational DNA repair, as well as to ensure accurate sister chromatid segregation in anaphase. Both of these roles are essential to genome stability.