Non-coding RNAs: novel players in chromatin-regulation during viral latency

Chromatin structure plays an essential role during gene expression regulation not only in the case of the host cellular genome, but also during the viral life cycle. Epigenetic chromatin marks thereby define, whether a gene promoter is accessible for the transcription machinery or whether a repressive heterochromatin state is established. The heterochromatin-mediated repression of lytic viral genes results in viral latency, enabling the virus to persist dormant without being recognized by the host immune system, but keeping the potential for reactivation. Arising new systems biology approaches are starting to uncover an unexpected multiplicity and variety of non-coding (nc)RNAs playing important roles during chromatin structure control, likely constituting a novel layer in epigenetic regulation. In this review we give an overview of chromatin-regulatory viral and host cellular ncRNAs and their links to viral latency.