Nucleic Acids Research Advance Access originally published online on November 22, 2007
Nucleic Acids Research 2008 36(2):364-375; doi:10.1093/nar/gkm991
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Nucleic Acids Research, 2008, Vol. 36, No. 2 364-375
© 2007 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Rho-independent transcription terminators inhibit RNase P processing of the secG leuU and metT tRNA polycistronic transcripts in Escherichia coli
Department of Genetics, University of Georgia, Athens, GA 30602, USA
*To whom correspondence should be addressed. Tel: +1 706 542 8000; Fax: +1 706 542 3910; Email: skushner{at}uga.edu
Received August 6, 2007. Revised October 17, 2007. Accepted October 22, 2007.
The widely accepted model for the processing of tRNAs in Escherichia coli involves essential initial cleavages by RNase E within polycistronic transcripts to generate pre-tRNAs that subsequently become substrates for RNase P. However, recently we identified two polycistronic tRNA transcripts whose endonucleolytic processing was solely dependent on RNase P. Here we show that the processing of the secG leuU and metT leuW glnU glnW metU glnV glnX polycistronic transcripts takes place through a different type of maturation pathway. Specifically, RNase P separates the tRNA units within each operon following the endonucleolytic removal of the distal Rho-independent transcription terminator, primarily by RNase E. Failure to remove the Rho-independent transcription terminator inhibits RNase P processing of both transcripts leading to a decrease in mature tRNA levels and dramatically increased levels of full-length transcripts in an RNase E deletion strain. Furthermore, we show for the first time that RNase G also removes the Rho-independent transcription terminator associated with the secG leuU operon. Our data also demonstrate that the Rne-1 protein retains significant activity on tRNA substrates at the non-permissive temperature. Taken together it is clear that there are multiple pathways involved in the maturation of tRNAs in E. coli.
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