Everywhere you look, be it Science or Nature, US Weekly (OK, not quite), silencing by ncRNAs is making headlines. But the targets and mechanisms of this silencing are not always clear. A recent report by Peter Fraser and co-workers at The Babraham Institute (UK) and several other universities and centers in Japan and Europe has revealed that a long (>200-nt) ncRNA called Air silences a target gene by recruiting the G9a histone methyltransferase to chromatin.
Air an imprinted ncRNA that is expressed from the paternal allele is required for allele-specific silencing of a cluster of imprinted genes in mouse placenta. The researchers found that, similar to Xist ncRNA on the X chromosome, Air “coats” the chromatin of the paternal Sle22a3 gene under conditions of gene silencing. The accumulation of Air at the Sle22a3 promoter was linked to increased tri-methylation of histone H3 lysine 9, a modification that is typical of repressed chromatin. The investigators further showed that Air silences the paternal Sle22a3 gene by targeting G9a to chromatin.
To see why this paper deserves plenty of Air time, go to Science, Nov 2008.