title: The MiaA tRNA modification enzyme is necessary for robust RpoS expression in Escherichia coli.
abstract: The stationary phase/general stress response sigma factor RpoS (σ(S)) is necessary for adaptation and restoration of homeostasis in stationary phase. As a physiological consequence, its levels are tightly regulated at least at two levels. Multiple small regulatory RNA molecules modulate its translation, in a manner that is dependent on the RNA chaperone Hfq and the rpoS 5' untranslated region. ClpXP and the RssB adaptor protein degrade RpoS, unless it is protected by an anti-adaptor. We here find that, in addition to these posttranscriptional levels of regulation, tRNA modification also affects the steady-state levels of RpoS. We screened mutants of several RNA modification enzymes for an effect on RpoS expression and identified the miaA gene, encoding a tRNA isopentenyltransferase, as necessary for full expression of both an rpoS750-lacZ translational fusion and the RpoS protein. This effect is independent of rpoS, the regulatory RNAs, and RpoS degradation. RpoD steady-state levels were not significantly different in the absence of MiaA, suggesting that this is an RpoS-specific effect. The rpoS coding sequence is significantly enriched for leu codons that use MiaA-modified tRNAs, compared to rpoD and many other genes. Dependence on MiaA may therefore provide yet another way for RpoS levels to respond to growth conditions.
authors.affiliation: Department of Microbiology, College of Medicine, Howard University, Washington, DC, USA.
authors.forename: Karl M
authors.initials: KM
authors.lastname: Thompson
authors.forename: Susan
authors.initials: S
authors.lastname: Gottesman
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000096:biosynthesis*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D015964:Gene Expression Regulation, Bacterial; D012343:RNA, Transfer / Q000378:metabolism*; D012808:Sigma Factor / Q000096:biosynthesis*
chemical_list: D001426:Bacterial Proteins; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria; D012343:RNA, Transfer; D019883:Alkyl and Aryl Transferases; C024274:adenylate isopentenyltransferase