Positions of Trp Codons in the Leader Peptide-Coding Region of the at Operon Influence Anti-Trap Synthesis and trp Operon Expression in Bacillus licheniformis

Department of Biology, Stanford University, Stanford, CA 94305, USA.
Journal of bacteriology (Impact Factor: 2.81). 03/2010; 192(6):1518-26. DOI: 10.1128/JB.01420-09
Source: PubMed


Tryptophan, phenylalanine, tyrosine, and several other metabolites are all synthesized from a common precursor, chorismic
acid. Since tryptophan is a product of an energetically expensive biosynthetic pathway, bacteria have developed sensing mechanisms
to downregulate synthesis of the enzymes of tryptophan formation when synthesis of the amino acid is not needed. In Bacillus subtilis and some other Gram-positive bacteria, trp operon expression is regulated by two proteins, TRAP (the tryptophan-activated RNA binding protein) and AT (the anti-TRAP
protein). TRAP is activated by bound tryptophan, and AT synthesis is increased upon accumulation of uncharged tRNATrp. Tryptophan-activated TRAP binds to trp operon leader RNA, generating a terminator structure that promotes transcription termination. AT binds to tryptophan-activated
TRAP, inhibiting its RNA binding ability. In B. subtilis, AT synthesis is upregulated both transcriptionally and translationally in response to the accumulation of uncharged tRNATrp. In this paper, we focus on explaining the differences in organization and regulatory functions of the at operon's leader peptide-coding region, rtpLP, of B. subtilis and Bacillus licheniformis. Our objective was to correlate the greater growth sensitivity of B. licheniformis to tryptophan starvation with the spacing of the three Trp codons in its at operon leader peptide-coding region. Our findings suggest that the Trp codon location in rtpLP of B. licheniformis is designed to allow a mild charged-tRNATrp deficiency to expose the Shine-Dalgarno sequence and start codon for the AT protein, leading to increased AT synthesis.

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Available from: Anastasia Levitin, Sep 24, 2015