Toward a consensus on the binding specificity and promiscuity of PRC2 for RNA.

Polycomb repressive complex-2 (PRC2) is a histone methyltransferase required for epigenetic silencing during development and cancer. Early works suggested binding specificity of PRC2 to certain long non-coding RNAs for recruitment to chromatin. More recent studies provided evidence both in favor and against this idea. Here, we bridge the two existing models of PRC2-RNA interaction. RepA RNA is a good binding partner for PRC2, while multiple non-relevant RNAs, including bacterial mRNAs, also bind PRC2; Kds depend to some extent on the experimental conditions. Human and mouse PRC2 have broadly similar RNA-binding properties in vitro. Examination of evidence supporting an existing model for site-specific recruitment of PRC2 by a well-defined RNA motif in cells reveals that results are PRC2 independent. We conclude that promiscuous and specific RNA-binding activities of PRC2 in vitro are not mutually exclusive, and that binding specificity in vivo remains to be demonstrated.
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