Targeting of cohesin by transcriptionally silent chromatin.
Eukaryotic DNA replication produces sister chromatids that are linked together until anaphase by cohesin, a ring-shaped protein complex that is thought to act by embracing both chromatids. Cohesin is enriched at centromeres, as well as discrete sites along chromosome arms where transcription positions the complex between convergent gene pairs. A relationship between cohesin and Sir-mediated transcriptional silencing has also begun to emerge. Here we used fluorescence microscopy and site-specific recombination to characterize interactions between newly replicated copies of the silent HMR mating-type locus. HMR was tagged with lac-GFP and flanked by binding sites for an inducible site-specific recombinase. Excision of the locus in cells with sister chromatids produced two chromatin circles that remained associated with one another. Pairing of the circles required silent chromatin, cohesin, and the RSC chromatin-remodeling complex. Chromatin immunoprecipitation showed that targeting of cohesin to the locus is Sir-dependent, and functional tests showed that silent chromatin acts in a continuous fashion to maintain cohesion. Remarkably, loss of silencing led to loss of cohesin from linear chromosomal templates but not from excised chromatin circles. The results are consistent with a model in which cohesin binds silent chromatin via topological linkage to individual chromatids.
Chang
Chuang-Rung
CR
Department of Pharmacology, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, 08854, USA.
Wu
Ching-Shyi
CS
Hom
Yolanda
Y
Gartenberg
Marc R
MR
D018797:Cell Cycle Proteins / Q000378:metabolism*; D002842:Chromatids / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism*; D002868:Chromosomal Proteins, Non-Histone; D015825:Chromosomes, Fungal / Q000378:metabolism; D004261:DNA Replication / Q000502:physiology; D005656:Fungal Proteins / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal / Q000502:physiology*; D020868:Gene Silencing / Q000502:physiology; D049770:Genes, Mating Type, Fungal / Q000502:physiology*; D009687:Nuclear Proteins / Q000378:metabolism*; D040641:Quantitative Trait Loci / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000502:physiology*; D000097722:Cohesins
D018797:Cell Cycle Proteins; D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; D005656:Fungal Proteins; D009687:Nuclear Proteins; D000097722:Cohesins