Transcription attenuation in Salmonella typhimurium: the significance of rare leucine codons in the leu leader.
نویسندگان
چکیده
The leucine operon of Salmonella typhimurium is controlled by a transcription attenuation mechanism. Four adjacent leucine codons within a 160-nucleotide leu leader RNA are thought to play a central role in this mechanism. Three of the four codons are CUA, a rarely used leucine codon within enteric bacteria. To determine whether the nature of the leucine codon affects the regulation of the leucine operon, we used oligonucleotide-directed mutagenesis to first convert one CUA of the leader to CUG and then convert all three CUA codons to CUG. CUG is the most frequently used leucine codon in enteric bacteria. A mutant having (CUA)2CUGCUC in place of (CUA)3CUC has an altered response to leucine limitation, requiring a slightly higher degree of limitation to effect derepression. Changing (CUA)3CUC to (CUG)3CUC has more dramatic effects upon operon expression. First, the basal level of expression is lowered to the point that the mutant grows more slowly than the parent in a minimal medium lacking leucine. Second, the response of the mutant to a leucine limitation is dramatically altered such that even a strong limitation elicits only a modest degree of derepression. If the mutant is grown under conditions of leucyl-tRNA limitation rather than leucine limitation, complete derepression can be achieved, but only at a much higher degree of limitation than for the wild-type operon. These results provide a clear-cut example of codon usage having a dramatic effect upon gene expression.
منابع مشابه
Transcription attenuation-mediated control of leu operon expression: influence of the number of Leu control codons.
Four adjacent Leu codons within the leu leader RNA are critically important in transcription attenuation-mediated control of leu operon expression in Salmonella typhimurium and Escherichia coli (P. W. Carter, D. L. Weiss, H. L. Weith, and J. M. Calvo, J. Bacteriol. 162:943-949, 1985). The leader region from S. typhimurium was altered by site-directed mutagenesis to produce constructs having bet...
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عنوان ژورنال:
- Proceedings of the National Academy of Sciences of the United States of America
دوره 83 21 شماره
صفحات -
تاریخ انتشار 1986