Nucleic Acids Research Advance Access published online on November 11, 2009
Nucleic Acids Research, doi:10.1093/nar/gkp997
Nucleic Acid Enzymes |
Processing of the Escherichia coli leuX tRNA transcript, encoding tRNALeu5, requires either the 3'
5' exoribonuclease polynucleotide phosphorylase or RNase P to remove the Rho-independent transcription terminator
Department of Genetics, University of Georgia, Athens, GA 30605, USA
*To whom correspondence should be addressed. Tel: +1 706 542 8000; Fax: +1 706 542 3910; Email: skushner{at}uga.edu
Received September 21, 2009. Revised October 15, 2009. Accepted October 16, 2009.
Here we report a unique processing pathway in Escherichia coli for tRNALeu5 in which the exoribonuclease polynucleotide phosphorylase (PNPase) removes the Rho-independent transcription terminator from the leuX transcript without requiring the RhlB RNA helicase. Our data demonstrate for the first time that PNPase can efficiently degrade an RNA substrate containing secondary structures in vivo. Furthermore, RNase P, an endoribonuclease that normally generates the mature 5'-ends of tRNAs, removes the leuX terminator inefficiently independent of PNPase activity. RNase P cleaves 4–7 nt downstream of the CCA determinant generating a substrate for RNase II, which removes an additional 3–4 nt. Subsequently, RNase T completes the 3' maturation process by removing the remaining 1–3 nt downstream of the CCA determinant. RNase E, G and Z are not involved in terminator removal. These results provide further evidence that the E. coli tRNA processing machinery is far more diverse than previously envisioned.