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J. Bacteriol., 11 1995, 6362-6370, Vol 177, No. 22
E Merino, P Babitzke and C Yanofsky
Expression of the Bacillus subtilis trpEDCFBA operon has been shown to be
regulated by transcription attenuation in response to the availability of
L-tryptophan. Regulation is mediated by the tryptophan- activated trp
RNA-binding attenuation protein, TRAP, the product of mtrB. Formation of
mutually exclusive RNA anti-terminator and terminator structures within trp
leader RNA determines whether transcription will terminate in the leader
region of the operon. Previous studies suggested that transcripts that
escape termination are subject to translational regulation via the
formation of a secondary structure that blocks ribosome access to the trpE
ribosome-binding site. To assess the relative importance of these
postulated events in trp operon regulation, we used site-directed
mutagenesis to alter the putative elements involved in transcriptional and
translational control. Using a trpE'-'lacZ reporter, we measured
translational yield and specific mRNA levels with various leader
constructs, in both mtrB+ and mtrB strains, during growth in the presence
and absence of excess tryptophan. To verify that the altered regulatory
regions behaved as expected, we carried out in vitro transcription assays
with the wild- type and altered leader region templates and performed
oligonucleotide competition assays with an oligonucleotide complementary to
a segment of the transcription terminator. Our results establish that
binding of TRAP to leader RNA regulates of transcription termination in the
trp operon over about an 88-fold range and regulates translation of trpE
over about a 13-fold range. The roles played by different trp leader RNA
segments in mediating transcriptional and translational regulation are
documented by our findings.
Copyright © 1995, American Society for Microbiology
trp RNA-binding attenuation protein (TRAP)-trp leader RNA interactions mediate translational as well as transcriptional regulation of the Bacillus subtilis trp operon
Department of Biological Sciences, Stanford University, California 94305, USA.
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