However, the enzyme is not essential AMN-107 cost for growth of E. coli in rich or minimal media . Queuosine is widely distributed in bacteria, and it is present in the first base of the anticodon of tRNAAsp, tRNAAsn, tRNAHis and tRNATyr; however in E. coli only tRNAAsp is a substrate for the GluQ-RS enzyme. The presence of modifications within the anticodon loop of the tRNA, could enhance the accuracy of the codon binding . Then the tRNAAspQ34 might improve recognition of both GAC and GAU codons
 and stimulate the binding of the GAU codon to the ribosome . In Shigella flexneri it has been shown that mutations in genes required for tRNA modifications, miaA and tgt decreased virulence. miaA is required for 2-methylthio-N6-isopentenyladenosine modification at position 37 of the anticodon loop and tgt is involved in queuosine modification at position 34 within the anticodon loop [16–18]. In this study, we determined the role of the genome organization and its effect on the expression of the gluQ-rs gene in the major human pathogen, S. flexneri. Results Genomic organization of the S. flexneri gluQ-rs gene GluQ-RS is required for the synthesis of the modified nucleoside, GluQ, present on tRNAAsp[10,
11]. By searching the bacterial protein database Uniprot (http://www.uniprot.org/), we were able to identify GluQ-RS in more than a hundred bacterial species, primarily proteobacteria (C646 Figure 1, filled symbols). From the phylogenetic analysis we can distinguished the three subgroups of enzymes described by Dubois et al., 2004 , which are characterized by the presence of the signature HXGS, P505-15 molecular weight HXGN or HXGH in the adenylate binding site. A similar tree was obtained using the Neighbor joining method. Phylogenetic analysis within the subgroup of enzymes with the HXGN motif, included
representatives from the Firmicutes bacterial group (Figure 1, open square) together with Desulfovibrio vulgaris and Truepera radiovictrix enzymes. From the alignment, these members have 8 characteristic amino acids, G70PDXGGXX, that do not align with the other GluQ-RS (Figure 1, numbering is derived from D. vulgaris enzyme). Further genomic analysis indicated that the gluQ-rs gene is found primarily in two genomic arrangements, either alone or located immediately downstream of dksA. Searching within the String database  and GenomeNet Methane monooxygenase , we found that the dksA gluQ-rs gene organization was conserved in more than 40 different species, all of which were within the gammaproteobacteria group. These included species of Aeromonadales, Alteromonadales, Enterobacteriaceae, including E. coli and S. flexneri, Pseudomanadales, and Vibrionaceae (Figure 1). Figure 1 GluQ-RS is distributed within the bacterial domain. Rooted Phylogenetic analysis of selected sequences of GluQ-RS, showing the presence of this enzyme in the bacterial domain. Searching within the Uniprot database (http://www.uniprot.