cereus may have evolved from an element with a specificity

determinant similar in sequence to that of lysine. These observations suggest that T box regulation may be unsuited for controlling expression of the housekeeping LysRS in bacteria and perhaps is only tolerated in additional copies of LysRS that play an ancillary role such as ATR inhibitor adaptation to stationary phase conditions as observed in B. cereus. Determining whether the other T box regulated lysS genes play an ancillary role requires Staurosporine mw further investigation. Notably, T box regulation of housekeeping aminoacyl tRNA synthetases is widespread, suggesting that it is some aspect of lysine metabolism that makes T box control of LysRS expression unsuitable as a regulatory mechanism. The LysRS1 T box element from B. cereus is functional and B. subtilis strains with T box control of LysRS1 and LysR2 expression are viable The unknown provenance and functionality of the T box element, BAY 11-7082 despite the reported theoretical capability to form canonical T box element structures [8] prompted us to verify that it was functional and to ask whether strains of B. subtilis expressing a single copy of LysRS1 or LysRS2 controlled by this T box element are viable. We chose to conduct this study in B. subtilis because of the paucity of relevant auxotrophic B. cereus strains and other difficulties with antibiotic resistance and transformability.

However we consider B. subtilis to be a valid model system in which to conduct this study. Our results show that the T box element 3-oxoacyl-(acyl-carrier-protein) reductase is functional and can be induced up to 120-fold in response to lysine- or LysRS-depletion but not by depletion of non-cognate amino acids. Also strains of B. subtilis with expression of the endogenous LysRS2 controlled by this T box element are viable, and could not be distinguished from B. subtilis wild-type strain 168 during growth in rich or minimal medium. While a strain of B. subtilis expressing LysRS1 controlled by the T box element from B. cereus strain 14579 is also viable, it displays a growth defect when grown in rich

medium and cannot be propagated in minimal medium. However it is likely that these phenotypes result from the reduced catalytic activity of class I LysRS enzyme rather than from control of expression by the T box element. These results show there is no a priori reason precluding control of LysRS expression by a tRNALys-responsive T box element. It emphasizes the puzzling rarity of T box regulated LysRS expression and the restriction of its occurrence in B. cereus strain 14579 to controlling expression of a LysRS1 enzyme that plays an ancillary role in adapting cells to adverse conditions. The T box element controlling expression of LysRS1 in B. cereus strain 14579 can be induced by an increased level of uncharged tRNAAsn The unusual occurrence of tRNALys-responsive T box elements and the experimentally demonstrated viability of B.

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