polyloop · Policing mammalian transcriptomes: regulation of long ncRNA synthesis by transcriptional termination, gene loops and R-loops

.Mammalian transcriptome analysis reveals that while most of the genome is transcribed, only a minority fraction produces protein coding, messenger RNA or functional, structural RNA. Instead a substantial fraction is transcribed, often tissue specifically, into long non coding (lnc)RNA of mostly unknown function. Many lncRNA are rapidly degraded and may reflect promiscuous, non-functional transcription. However some lncRNA have important cellular functions. I reason that defining promoters and terminators of lncRNA genes will provide valuable information on which lncRNA are likely to be functional. LncRNA gene promoters often correspond to nucleosome depleted regions of protein coding gene promoters and enhancers, which generate bidirectional transcription. Regions of single-strand DNA, exposed by R-loop formation can also initiate transcription and so act as a potential source of lncRNA, as will be investigated here. Since transcription initiation of lncRNA genes appears relatively promiscuous, terminating lncRNA transcription may be of critical importance. This will prevent read-through transcription with consequent negative affects on downstream genes by transcriptional interference or the formation of overlapping transcripts leading to RNA interference effects. Consequently I will focus on transcription termination mechanisms of lncRNA genes. I will determine if known protein coding gene terminators also operate for lncRNA genes or whether many lncRNA use alternative termination mechanisms. In particular I will investigate the role of G-rich pausing elements that promote Pol II termination by forming R-loop structures on lncRNA genes. I will also investigate which classes of lncRNA genes form gene loop conformations when transcribed, as a likely identifier of more highly expressed, functional lncRNA. Overall I predict that understanding how lncRNA are synthesised will provide critical information on which lncRNA warrant scrutiny as likely functional transcripts