Nucleic Acids Res. 2011 Mar 17. [Epub ahead of print]
Widespread occurrence of non-canonical transcription termination by human RNA polymerase III.
Dipartimento di Biochimica e Biologia Molecolare, Università degli Studi di Parma, Viale G.P. Usberti 23/A, 43100 Parma, Italy, Institut Européen de Chimie et Biologie, Université de Bordeaux 2, Institut National de la Santé et de la Recherche Médicale (INSERM) U869, 33607 Pessac, France, Department of Microbiology, Denver School of Medicine, University of Colorado, Aurora, CO 80045, USA and Faculty of Biology and Medicine, Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland.
Human RNA polymerase (Pol) III-transcribed genes are thought to share a simple termination signal constituted by four or more consecutive thymidine residues in the coding DNA strand, just downstream of the RNA 3′-end sequence. We found that a large set of human tRNA genes (tDNAs) do not display any T(≥4) stretch within 50 bp of 3′-flanking region. In vitro analysis of tDNAs with a distanced T(≥4) revealed the existence of non-canonical terminators resembling degenerate T(≥5) elements, which ensure significant termination but at the same time allow for the production of Pol III read-through pre-tRNAs with unusually long 3′ trailers. A panel of such non-canonical signals was found to direct transcription termination of unusual Pol III-synthesized viral pre-miRNA transcripts in gammaherpesvirus 68-infected cells. Genome-wide location analysis revealed that human Pol III tends to trespass into the 3′-flanking regions of tDNAs, as expected from extensive terminator read-through. The widespread occurrence of partial termination suggests that the Pol III primary transcriptome in mammals is unexpectedly enriched in 3′-trailer sequences with the potential to contribute novel functional ncRNAs.
PMID: 21421562 [PubMed – as supplied by publisher]