Modulation of chromatin modifying complexes by noncoding RNAs in trans

Increasing evidence supports a central role for ncRNA in numerous aspects of chromatin function. For instance, ncRNAs can act as a scaffold for the recruitment of certain chromatin modifying complexes to specific sites within the genome. It is easily imaginable how this can occur in cis, but examples also exist whereby targeting of complexes by ncRNA occurs in trans to the site of transcription. Moreover, association of an ncRNA with a particular locus can trigger localization of the gene to a subnuclear structure harboring a specialized transcriptional environment. In this review, we discuss new insights into the mechanisms by which ncRNAs function in trans with respect to Polycomb Group, chromatin insulator, and dosage compensation complexes in mammals and/or Drosophila.