The recruitment of chromatin modifiers by long noncoding RNAs: lessons from PRC2

Polycomb repressive complex-2 (PRC2) is a histone methyltransferase required for epigenetic silencing during development and cancer. Among chromatin modifying factors shown to be recruited and regulated by long noncoding RNAs (IncRNAs), PRC2 is one of the most studied. Mammalian PRC2 binds thousands of RNAs in vivo, and it is becoming a model system for the recruitment of chromatin modifying factors by RNA. Yet, well-defined PRC2-binding motifs within target RNAs have been elusive. From the protein side, PRC2 RNA-binding subunits contain no known RNA-binding domains, complicating functional studies. Here we provide a critical review of existing models for the recruitment of PRC2 to chromatin by RNAs. This discussion may also serve researchers who are studying the recruitment of other chromatin modifiers by IncRNAs.