This is consistent with our results, in which we did not detect any activity from promoters other than those upstream of the dksA gene (Figure 3). This unusual arrangement suggests that

gluQ-rs expression is dependent on dksA-regulated conditions. Because DksA is a key member of the selleck compound stringent response in bacteria and regulates a number of processes in the cell, including its own expression [25, 28], the data suggest that there is coordinate regulation of tRNA modification and other DksA targets. Although we could not detect any promoter activity specific for gluQ-rs in the growth conditions tested (i.e. altering the pH, presence of glutamate), we cannot CFTRinh-172 discount the possibility that the gene is specifically regulated under some other conditions. The regulon database (http://​regulondb.​ccg.​unam.​mx/​index.​jsp) indicates that the E. coli gluQ-rs gene has a recognition site for the σ24 subunit of RNA polymerase. From our analysis, this sequence check details is identical to S. flexneri, but there is no experimental evidence of this recognition. Interestingly, when the gluQ-rs gene was deleted in S. flexneri, the mutant showed impaired growth in the presence of osmolytes (Figure 6). A recent publication demonstrated that σ24 and σS proteins from Salmonella enterica serovar Typhi are important

for the expression of several genes induced by osmotic stress in this bacterium [29]. Moreover, the expression of the gene encoding σ24 in E. coli is regulated by the stringent response [30]. The possible role of σ24 on the expression of gluQ-rs under osmotic stress might be interesting to study. GluQ-RS is an enzyme responsible for the formation of the GluQ tRNA modification, and two

independent groups [10, 11] have shown that this enzyme required a high concentration of glutamate to be activated and transferred to the queuosine base present on the tRNAAsp. Interestingly, one of the first events to occur when bacteria are subject to high osmolyte stress is an increase in glutamate levels within the cytoplasm [31]. Our observation indicates an important role of the tRNA modification for the growth of S. flexneri in the presence of osmolytes (Figure 6). Other tRNA modifications might play a similar role in this stress condition. In E. coli, inactivation of the Cepharanthine yfiC gene, responsible for the modification at the adenosine 37 present on the tRNAVal, leads to a high sensitivity to osmotic stress [32]. Transcription of gluQ-rs is regulated by a terminator The results obtained in the present work show the presence of a terminator and suggested the functionality of this structure (Figure 3 and Figure 4). To our knowledge, there are few examples of bacterial genes that have similar structures. There is a terminator structure upstream of the DNA primase gene, dnaG, which also has an unusual Shine Dalgarno sequence [33]. Another example is the recX gene in E.