This experiment highlights an additional difference between E. coli and S. aureus ribosomes. While lack of methylation by KsgA leads to increased sensitivity to the 4,6 class of aminoglycosides in both organisms, we see opposite effects on 4,5 aminoglycoside sensitivity. Both the KsgA target

site and the aminoglycoside binding site are among the most highly conserved rRNA sequences; JQEZ5 datasheet it is thus intriguing that distinct effects are seen between the two organisms. Although ribosome biogenesis has not been well-studied outside of the model RG7420 cell line organisms E. coli and, to a much lesser extent, B. subtilis, it is possible that reported differences in ribosome biogenesis between Gram-negative and Gram-positive organisms are representative of an evolutionary divergence between the two groups of bacteria. One such difference is the case of the ribonuclease RNase III. RNase III is an endonuclease that is involved in processing of the pre-rRNA transcript in both E. coli and B. subtilis. However, this enzyme is strictly essential in B. subtilis but not in E. coli[12]. Additionally, inactivation of RNase III has different effects on the maturation of 16S rRNA in the two organisms [12]. Further work is required to demonstrate whether these results are more broadly applicable in other bacterial species. Our work suggests differences in ribosome biogenesis between E. coli EVP4593 cost and S. aureus; it remains to be

seen if the differing reliance on KsgA can be defined by a phylogenetic Gram-positive/Gram-negative split. KsgA plays a key role in ribosome biogenesis in E. coli, which cannot be separated from its methyltransferase function [3]. Further evidence of KsgA’s significance in Gram-negative organisms comes from virulence studies in pathogenic organisms. Disruption of ksgA in Y. pseudotuberculosis confers almost an attenuated virulence phenotype on the knockout strain [6], and this attenuated

strain confers protection against subsequent challenge with the wild-type strain [13]. Additionally, mutation of ksgA in the plant pathogen E. amylovora decreases virulence [8] and disruption of KsgA in S. Enteriditis reduces invasiveness [14]. These studies affirm that KsgA may be a novel drug target in Gram-negative organisms. Studies on KsgA’s role in virulence have not been done in Gram-positive organisms, although in addition to the modest growth defects seen in the S. aureus ΔksgA strain disruption of the ksgA gene in the Gram-negative Mycobacterium tuberculosis was shown to negatively affect bacterial growth on solid media [5]. It should be noted that disruption of ksgA in Y. pseudotuberculosis produced only a slight growth defect and allowed the bacteria to survive in infected mice, even though the strain was not as virulent as the wild-type strain [6]. Likewise, E. amylovora mutants showed reduced virulence despite only small growth defects in vitro and the ability to grow in infected tissue [8].