A28
Investigating the interaction of cohesin with chromosomes
Maria TA Ocampo-Hafalla, Frank Uhlmann
Cancer Research UK, London Research Institute, London, UK
The ring-like cohesin complex physically links the sister chromatids to prevent their premature separation during cell division. However, despite cohesin’s importance in chromosomal stability, many aspects of its interaction with chromosomes have yet to be elucidated. Using S. cerevisiae as a model organism, we have previously observed that cohesin relocates from its initial binding sites and accumulates at sites of convergent transcriptional termination. Moreover, changes in transcriptional status affect cohesin localization, with the induction of a silent gene resulting in cohesin’s downstream repositioning. To investigate the nature of cohesin binding to chromosomes in vivo, we characterized the translocation of cohesin along model loci. Sites of cohesin localization were identified by chromatin immunoprecipitation followed by hybridization to oligonucleotide microarrays (ChIP-chip). We observed downstream repositioning of cohesin, albeit with reduced efficiency, after the inactivation of the Scc2/4 cohesin loading complex. However, induction levels of the model loci were also diminished in the Scc2/4 mutant cells. We also found that the pool of downstream relocated cohesin was composed of previously chromosome-bound rather than ectopically-expressed newly loaded cohesin. Finally, ‘loading-defective’ cohesin was able to translocate normally upon transcriptional activation. Current experiments are aimed at further examining the role of transcription in cohesin translocation. Since cohesin is essential for mediating chromosome stability during cell division, these findings will provide important insights about the mechanisms underlying the chromosomal instabilities observed in cancer.
