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Absence of RNase III alters the pathway by which RNAI, the antisense inhibitor of ColE1 replication, decays

Institute of Cell and Molecular Biology, University of Edinburgh, The King’s Buildings, Mayfield Road, Edinburgh EH9 3JR, UK¹

Author for correspondence: Millicent Masters. Tel: +44 131 650 5355. Fax: +44 131 650 8650. e-mail: M.Masters{at}ed.ac.uk

RNAI is a short RNA, 108 nt in length, which regulates the replication of the plasmid ColE1. RNAI turns over rapidly, enabling plasmid replication rate to respond quickly to changes in plasmid copy number. Because RNAI is produced in abundance, is easily extracted and turns over quickly, it has been used as a model for mRNA in studying RNA decay pathways. The enzymes polynucleotide phosphorylase, poly(A) polymerase and RNase E have been demonstrated to have roles in both messenger and RNAI decay; it is reported here that these enzymes can work independently of one another to facilitate RNAI decay. The roles in RNAI decay of two further enzymes which facilitate mRNA decay, the exonuclease RNase II and the endonuclease RNase III, are also examined. RNase II does not appear to accelerate RNAI decay but it is found that, in the absence of RNase III, polyadenylated RNAI, unprocessed by RNase E, accumulates. It is also shown that RNase III can cut RNAI near nt 82 or 98 in vitro. An RNAI fragment corresponding to the longer of these can be found in extracts of an rnc⁺ pcnB strain (which produces RNase III) but not of an rnc pcnB strain, suggesting that RNAI may be a substrate for RNase III in vivo. A possible pathway for the early steps in RNAI decay which incorporates this information is suggested.

Keywords: Escherichia coli, plasmid replication, RNA degradation, ribonuclease III, RNAI

Abbreviations: PAP I, poly(A) polymerase; PNPase, polynucleotide phosphorylase; RIF, rifampicin

^a Present address: Inveresk Research International Ltd, Tranent, East Lothian, UK.

^b Present address: Asthma Genetics Group, Nuffield Department of Clinical Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, UK.

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				Z. Wang, Z. Yuan, L. Xiang, J. Shao, and G. Wegrzyn tRNA-dependent cleavage of the ColE1 plasmid-encoded RNA I Microbiology, December 1, 2006; 152(12): 3467 - 3476. [Abstract] [Full Text] [PDF]