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Increased RNA polymerase availability directs resources towards growth at the expense of maintenance.

Journal article
Authors Bertil Gummesson
Lisa U. Magnusson
Martin Lovmar
Kristian Kvint
Örjan Persson
Manuel Ballesteros
Anne Farewell
Thomas Nyström
Published in The EMBO journal
Volume 28
Issue 15
Pages 2209-2219
ISSN 1460-2075
Publication year 2009
Published at Department of Cell and Molecular Biology
Department of Cell and Molecular Biology, Microbiology
Pages 2209-2219
Language en
Links dx.doi.org/10.1038/emboj.2009.181
Keywords RNA polymerase, transcriptional trade-off, stringent control, ppGpp, passive regulation
Subject categories Biological Sciences, Molecular biology

Abstract

Nutritionally induced changes in RNA polymerase availability have been hypothesized to be an evolutionary primeval mechanism for regulation of gene expression and several contrasting models have been proposed to explain how such 'passive' regulation might occur. We demonstrate here that ectopically elevating Escherichia coli RNA polymerase (Esigma(70)) levels causes an increased expression and promoter occupancy of ribosomal genes at the expense of stress-defense genes and amino acid biosynthetic operons. Phenotypically, cells overproducing Esigma(70) favours growth and reproduction at the expense of motility and damage protection; a response reminiscent of cells with no or diminished levels of the alarmone guanosine tetraphosphate (ppGpp). Consistently, we show that cells lacking ppGpp displayed markedly elevated levels of free Esigma(70) compared with wild-type cells and that the repression of ribosomal RNA expression and reduced growth rate of mutants with constitutively elevated levels of ppGpp can be suppressed by overproducing Esigma(70). We conclude that ppGpp modulates the levels of free Esigma(70) and that this is an integral part of the alarmone's means of regulating a trade-off between growth and maintenance.

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