Abstract
The ring-shaped cohesin complex is thought to topologically hold sister chromatids together from their synthesis in S phase until chromosome segregation in mitosis. How cohesin stably binds to chromosomes for extended periods, without impeding other chromosomal processes that also require access to the DNA, is poorly understood. Budding yeast cohesin is loaded onto DNA by the Scc2–Scc4 cohesin loader at centromeres and promoters of active genes, from where cohesin translocates to more permanent places of residence at transcription termination sites. Here we show that, at the GAL2 and MET17 loci, pre-existing cohesin is pushed downstream along the DNA in response to transcriptional gene activation, apparently without need for intermittent dissociation or reloading. We observe translocation intermediates and find that the distribution of most chromosomal cohesin is shaped by transcription. Our observations support a model in which cohesin is able to slide laterally along chromosomes while maintaining topological contact with DNA. In this way, stable cohesin binding to DNA and enduring sister chromatid cohesion become compatible with simultaneous underlying chromosomal activities, including but maybe not limited to transcription.
Highlights
Cohesin is a ring-shaped multi-subunit protein complex, which is best known for its essential role in promoting sister chromatid cohesion [1,2,3,4]
Scc3 in turn associates with Scc1 and plays an essential role in loading of the cohesin complex onto DNA [7,8]. It does so by providing interactions with a separate cohesin loader complex that in budding yeast consists of the Scc2 and Scc4 subunits [9]. In addition to this cohesin core machinery, additional subunits Pds5, Wapl and sororin, the latter restricted to higher eukaryotes, associate with the cohesin complex to regulate the stability of cohesin binding to chromosomes
There, as an exception to the typical location of cohesin peaks at convergent intergenic regions, three sequential genes in tandem orientation, SIC1, EMP46 and GAL2 are covered by cohesin
Summary
Cohesin is a ring-shaped multi-subunit protein complex, which is best known for its essential role in promoting sister chromatid cohesion [1,2,3,4]. Scc in turn associates with Scc and plays an essential role in loading of the cohesin complex onto DNA [7,8]. It does so by providing interactions with a separate cohesin loader complex that in budding yeast consists of the Scc and Scc subunits [9]. In addition to this cohesin core machinery, additional subunits Pds, Wapl and sororin, the latter restricted to higher eukaryotes, associate with the cohesin complex to regulate the stability of cohesin binding to chromosomes
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