A study of the regulation of aminoacyl tRNA synthetase gene expression in Bacillus by T-box regulatory elements

THESIS 9332The T-box antitermination mechanism is commonly used for the regulation of aminoacyl tRNA synthetase gene expression in Gram positive bacteria. However, expression of lysyl tRNA synthetases is rarely controlled in this way. Bacillus cereus was found to contain a class I lysK gene which has a putative T-box regulatory element upstream (Ataide, et al, 2005). In this work we characterized the T-box regulatory element of lysK from B. cereus. Our results showed that it is functional and responsive to reduced charging of tRNA LYS. Our analysis of 891 sequenced bacterial genomes had shown that all 6 strains containing T-box regulated lysS/K gene also encoded another lysS/K gene in the genome. Work in B. cereus had previously shown that the T-box regulated lysK gene is expressed predominantly in stationary phase and does not charge tRNA LYS during exponential growth (Ataide, et al., 2005). This led us to investigate if a strain of B. subtilis, containing a single lysS/K gene, whose expression is controlled by a T-box mechanism was viable

The T box regulatory element controlling expression of the class I lysyl-tRNA synthetase of <it>Bacillus cereus </it>strain 14579 is functional and can be partially induced by reduced charging of asparaginyl-tRNA^Asn

<p>Abstract</p> <p>Background</p> <p>Lysyl-tRNA synthetase (LysRS) is unique within the aminoacyl-tRNA synthetase family in that both class I (LysRS1) and class II (LysRS2) enzymes exist. LysRS1 enzymes are found in <it>Archaebacteria </it>and some eubacteria while all other organisms have LysRS2 enzymes. All sequenced strains of <it>Bacillus cereus </it>(except AH820) and <it>Bacillus thuringiensis </it>however encode both a class I and a class II LysRS. The <it>lysK </it>gene (encoding LysRS1) of <it>B. cereus </it>strain 14579 has an associated T box element, the first reported instance of potential T box control of LysRS expression.</p> <p>Results</p> <p>A global study of 891 completely sequenced bacterial genomes identified T box elements associated with control of LysRS expression in only four bacterial species: <it>B. cereus, B. thuringiensis, Symbiobacterium thermophilum </it>and <it>Clostridium beijerinckii</it>. Here we investigate the T box element found in the regulatory region of the <it>lysK </it>gene in <it>B. cereus </it>strain 14579. We show that this T box element is functional, responding in a canonical manner to an increased level of uncharged tRNA^Lysbut, unusually, also responding to an increased level of uncharged tRNA^Asn. We also show that <it>B. subtilis </it>strains with T box regulated expression of the endogenous <it>lysS </it>or the heterologous <it>lysK </it>genes are viable.</p> <p>Conclusions</p> <p>The T box element controlling <it>lysK </it>(encoding LysRS1) expression in <it>B. cereus </it>strain 14579 is functional, but unusually responds to depletion of charged tRNA^Lysand tRNA^Asn. This may have the advantage of making LysRS1 expression responsive to a wider range of nutritional stresses. The viability of <it>B. subtilis </it>strains with a single LysRS1 or LysRS2, whose expression is controlled by this T box element, makes the rarity of the occurrence of such control of LysRS expression puzzling.</p