Transcriptional regulation through noncoding RNAs and epigenetic modifications.

The recognition that substantial portions of the "noncoding (nc)" regions of metazoan genomes are transcribed has generated intense interest in the potential biological roles of ncRNAs. Gene silencing has emerged as one of the major functions of short double stranded ncRNAs (22-25 nucleotides, nt) that are generated by specific processing machinery. Transcription is also regulated by other classes of ncRNAs, including long (more than 200 nt), single-stranded, polyadenylated RNA molecules. Here, we review recent studies suggesting that some ncRNAs appear to function by binding to and regulating the activities of transcriptional co-activator or co-repressor complexes. Although the extents to which these mechanisms are used remains to be established, the identification of highly conserved ncRNAs and the presence of RNA binding domains in a large number of transcriptional co-regulators raise the possibility that ncRNA/coregulator interactions play broad roles in the regulation of gene expression.