Molecular Biology

Polycomb Promiscuity

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Science  08 Nov 2013:
Vol. 342, Issue 6159, pp. 671
DOI: 10.1126/science.342.6159.671-d

Turning genes off when they are not needed is as important as turning them on when they are. The polycomb repressive complex 2 (PRC2) shuts down gene expression during development in multicellular eukaryotes, and aberrant regulation of it can contribute to cancer. PRC2 is recruited to repress specific genes via its interaction with long noncoding RNAs (lncRNAs) such as HOTAIR and RepA. Other evidence suggests that PRC2 can interact with very many RNAs, and Davidovich et al. have extended these latter observations to show that, in vitro, PRC2 can bind RNA promiscuously and with affinities similar to those of its specific interactions with HOTAIR and RepA. In an analysis of previously published data sets, they demonstrate that PRC2 can interact with both specific lncRNAs and with RNA transcripts from many highly expressed genes in vivo. Although many of the genes that PRC2 interacts with include repressive chromatin marks, as expected given its silencing activity, up to one-third contain only activating marks. The capacity to bind a variety of RNAs enables PRC2 to scan the chromatin of active genes for repressive marks, which would indicate that the genes have somehow escaped silencing, and to shut them down again.

Nat. Struct. Mol. Biol. 20, 10.1038/nsmb.2679 (2013).

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