Nature Genetics
37, 809 - 819 (2005)
Published online: 24 June 2005; | doi:10.1038/ng1602
Comprehensive analysis of heterochromatin- and RNAi-mediated epigenetic control of the fission yeast genomeHugh P Cam1, Tomoyasu Sugiyama1, Ee Sin Chen1, Xi Chen1, Peter C FitzGerald2
& Shiv I S Grewal11
Laboratory of Molecular Cell Biology, National Institutes of Health, Bethesda, Maryland 20892-4255, USA. 2
Genome Analysis Unit, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4255, USA.
Correspondence should be addressed to Shiv I S Grewal grewals@mail.nih.gov The organization of eukaryotic genomes into distinct structural and functional domains is important for the regulation and transduction of genetic information. Here, we investigated heterochromatin and euchromatin profiles of the entire fission yeast genome and explored the role of RNA interference (RNAi) in genome organization. Histone H3 methylated at Lys4, which defines euchromatin, was not only distributed across most of the chromosomal landscape but was also present at the centromere core, the site of kinetochore assembly. In contrast, histone H3 methylated at Lys9 and its interacting protein Swi6/HP1, which define heterochromatin, coated extended domains associated with a variety of repeat elements and small islands corresponding to meiotic genes. Notably, RNAi components were distributed throughout all these heterochromatin domains, and their localization depended on Clr4/Suv39h histone methyltransferase. Sequencing of small interfering RNAs (siRNAs) associated with the RITS RNAi effector complex identified hot spots of siRNAs, which mapped to a diverse array of elements in these RNAi-heterochromatin domains. We found that Clr4/Suv39h predominantly silenced repeat elements whose derived transcripts, transcribed mainly by RNA polymerase II, serve as a source for siRNAs. Our analyses also uncover an important role for the RNAi machinery in maintaining genomic integrity.
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