The mtr locus is a two-gene operon required for transcription attenuation in the trp operon of Bacillus subtilis.

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Abstract
We have cloned and characterized the mtr operon of Bacillus subtilis. This operon encodes a presumed RNA-binding regulatory protein that is required for attenuation control of the trp operon. We have shown that the mtr operon consists of two structural genes, mtr-A and mtrB, predicted to encode 22-kDa and 9-kDa polypeptides, respectively. MtrB shows homology with RegA, an RNA-binding regulatory protein of bacteriophage T4. The lesions in several mtr mutants were localized to mtrB or the putative mtr promoter. Several mtrB alleles were dominant to mtr+, suggesting that the regulatory factor is a multimeric protein. The in vivo action of the mtrA and mtrB gene products was analyzed in an Escherichia coli strain containing a trpE-lacZ gene fusion under control of the B. subtilis trp promoter/attenuator region. Both MtrA and MtrB were necessary for regulation of .beta.-galactosidase production.