Cruz-Vera Luis R, Yang Rui, Yanofsky Charles
Department of Biological Sciences, Stanford University, Stanford, CA 94305-5020, USA.
J Bacteriol. 2009 Nov;191(22):7001-6. doi: 10.1128/JB.01002-09. Epub 2009 Sep 18.
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.
大肠杆菌和普通变形杆菌的色氨酸操纵子的表达由L-色氨酸诱导。在大肠杆菌中，色氨酸的作用取决于新合成的TnaC前导肽WFNIDXXL/IXXXXP中几个关键残基（下划线标注）的存在。这些残基在普通变形杆菌和其他细菌物种的TnaC中是保守的。普通变形杆菌的TnaC有一个与大肠杆菌的TnaC不同的额外特征；在保守的脯氨酸残基之后，它含有两个C端赖氨酸残基。在本研究中，我们研究了转移到大肠杆菌质粒上的普通变形杆菌色氨酸操纵子的L-色氨酸诱导情况。结果表明诱导是依赖L-色氨酸的；然而，诱导范围小于大肠杆菌色氨酸操纵子所观察到的范围。我们比较了两个操纵子的基因组织，并预测了它们各自前导mRNA片段的相似折叠模式。然而，进一步的分析表明，普通变形杆菌色氨酸操纵子中L-色氨酸的作用涉及在脯氨酸添加后抑制TnaC的延伸，而不是抑制前导肽的终止。我们的研究结果还表明，普通变形杆菌TnaC中的保守残基对于L-色氨酸诱导和抑制肽延伸至关重要。因此，TnaC合成是研究肽终止和肽延伸调控以及核糖体识别新生肽特征的一个优秀模型系统。
