Regulation of the Escherichia coli tna operon: Nascent leader peptide control at the tnaC stop codon
Regulation of the Escherichia coli tna operon: Nascent leader peptide control at the tnaC stop codon
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DOI：
10.1128/jb.179.5.1774-1779.1997
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发表时间：
1997-03-01
影响因子：
3.2
通讯作者：
Yanofsky, C
中科院分区：
文献类型：
--
作者：
Konan, KV;Yanofsky, C
大肠杆菌tna操纵子的表达受降解代谢物阻遏和tna诱导的转录反终止作用的调控，其终止位点位于操纵子前导区的Rho依赖性终止位点。色氨酸诱导依赖于一个短的前导肽编码区tnaC的翻译，该编码区含有一个单一的、关键的色氨酸密码子。最近的研究表明，在诱导过程中，TnaC前导肽顺式作用于翻译核糖体，以抑制其在tnaC终止密码子处的释放。在本研究中，我们使用缺少tnaC-tnaA间隔区的tnaC-UGA-'lacZ构建体来分析TnaC合成对翻译tnaC的核糖体行为的影响，tnaC-UGA-' lacZ构建体。在存在或不存在诱导物的情况下不显著表达，然而，在存在UGA抑制剂的情况下，或当多肽释放因子3的结构基因被破坏时，或当野生型tRNA（Trp）过量产生时，其表达。在每种情况下，tnaC-UGA-'lacZ表达都因诱导水平的色氨酸的存在而明显降低。用有义密码子替换tnaC UGA终止密码子允许相当大的表达，通过添加色氨酸也降低了表达，尽管程度较低。当tnaC的Trp密码子12改变为Leu密码子时，未观察到色氨酸的抑制。从多拷贝质粒反式过表达tnaC可防止色氨酸对表达的抑制。这些结果支持了TnaC前导肽顺式作用改变thf翻译核糖体的行为的假设。
Expression of the tryptophanase (tna) operon of Escherichia coli is regulated bg catabolite repression and by tryptophan-induced transcription antitermination at Rho-dependent termination sites in the leader region of the operon. Tryptophan induction is dependent on translation of a short leader peptide coding region, tnaC, that contains a single, crucial tryptophan codon, Recent studies suggest that during induction, the TnaC leader peptide acts in cis on the translating ribosome to inhibit its release at the tnaC stop codon. In the present study we usf a tnaC-UGA-'lacZ construct lacking the tnaC-tnaA spacer region to analyze the effect of TnaC synthesis on the behavior of the ribosome that translates tnaC, The tnaC-UGA-'lacZ construct. is not expressed significantly in the presence or absence of inducer, However, it is expressed in the presence of UGA suppressors, or when the structural gene for polypeptide release factor 3 is disrupted, or when wild-type tRNA(Trp) is overproduced. In each situation, tnaC-UGA-'lacZ expression is reduced appreciably by the presence of inducing levels of tryptophan. Replacing the tnaC UGA stop codon with a sense codon allows considerable expression, which is also reduced, although to a Lesser extent, by the addition of tryptophan. Inhibition by tryptophan is not observed when Trp codon 12 of tnaC is changed to a Leu codon, Overexpression of tnaC in trans from a multicopy plasmid prevents inhibition of expression by tryptophan. These results support the hypothesis that the TnaC leader peptide acts in cis to alter thf behavior of thf translating ribosome.