| Summary: | <p>Abstract</p> <p>Background</p> <p>The tyramine producer <it>Enterococcus durans </it>IPLA655 contains all the necessary genes for tyramine biosynthesis, grouped in the TDC cluster. This cluster includes <it>tyrS</it>, an aminoacyl-tRNA synthetase like gene.</p> <p>Results</p> <p>This work shows that <it>tyrS </it>was maximally transcribed in absence of tyrosine at acidic pH, showing a greater than 10-fold induction in mRNA levels over levels occurring in presence of tyrosine. Mapping of the <it>tyrS </it>transcriptional start site revealed an unusually long untranslated leader region of 322 bp, which displays the typical features of the T box transcriptional attenuation mechanism. The tyrosine concentration regulation of <it>tyrS </it>was found to be mediated by a transcription antitermination system, whereas the specific induction at acidic pH was regulated at transcription initiation level.</p> <p>Conclusions</p> <p>The expression of the <it>tyrS </it>gene present in the TDC cluster of <it>E. durans </it>is transcriptionally regulated by tyrosine concentration and extracelular pH. The regulation is mediated by both an antitermination system and the promoter itself.</p>
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