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Journal of Bacteriology, November 2009, p. 7001-7006, Vol. 191, No. 22
0021-9193/09/$08.00+0     doi:10.1128/JB.01002-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Tryptophan Inhibits Proteus vulgaris TnaC Leader Peptide Elongation, Activating tna Operon Expression{triangledown}

Luis R. Cruz-Vera,2 Rui Yang,1 and Charles Yanofsky1*

Department of Biological Sciences, Stanford University, Stanford, California 94305-5020,1 Department of Biological Sciences, University of Alabama—Huntsville, Huntsville, Alabama 358992

Received 28 July 2009/ Accepted 12 September 2009

Expression of the tna operon of Escherichia coli and of Proteus vulgaris is induced by L-tryptophan. In E. coli, tryptophan action is dependent on the presence of several critical residues (underlined) in the newly synthesized TnaC leader peptide, WFNIDXXL/IXXXXP. These residues are conserved in TnaC of P. vulgaris and of other bacterial species. TnaC of P. vulgaris has one additional feature, distinguishing it from TnaC of E. coli; it contains two C-terminal lysine residues following the conserved proline residue. In the present study, we investigated L-tryptophan induction of the P. vulgaris tna operon, transferred on a plasmid into E. coli. Induction was shown to be L-tryptophan dependent; however, the range of induction was less than that observed for the E. coli tna operon. We compared the genetic organization of both operons and predicted similar folding patterns for their respective leader mRNA segments. However, additional analyses revealed that L-tryptophan action in the P. vulgaris tna operon involves inhibition of TnaC elongation, following addition of proline, rather than inhibition of leader peptide termination. Our findings also establish that the conserved residues in TnaC of P. vulgaris are essential for L-tryptophan induction, and for inhibition of peptide elongation. TnaC synthesis is thus an excellent model system for studies of regulation of both peptide termination and peptide elongation, and for studies of ribosome recognition of the features of a nascent peptide.

* Corresponding author. Mailing address: Department of Biological Sciences, Stanford University, Stanford, CA 94305. Phone: (650) 725-1835. Fax: (650) 725-8221. E-mail: yanofsky{at}stanford.edu

{triangledown} Published ahead of print on 18 September 2009.

Journal of Bacteriology, November 2009, p. 7001-7006, Vol. 191, No. 22
0021-9193/09/$08.00+0     doi:10.1128/JB.01002-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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