Article
- The EMBO Journal (2009) 28, 2209 - 2219
- doi:10.1038/emboj.2009.181
Published online: 2 July 2009
Subject Category:
Increased RNA polymerase availability directs resources towards growth at the expense of maintenance
Bertil Gummesson1,2, Lisa U Magnusson1,2, Martin Lovmar1,3, Kristian Kvint1, Örjan Persson1, Manuel Ballesteros1,4, Anne Farewell1 and Thomas Nyström1
- Department of Cell and Molecular Biology, Gothenburg University, Göteborg, Sweden
- These authors contributed equally to this work
Correspondence to:
Thomas Nyström, Department of Cell and Molecular Biology, Gothenburg University, Medicinaregatan 9C, Göteborg 41390, Sweden. Tel.: +46 31 786 2582; Fax: +46 31 786 2599; E-mail: thomas.nystrom@cmb.gu.se
Lisa U Magnusson, Department of Cell and Molecular Biology, Gothenburg University, Medicinaregatan 9C, Göteborg 41390, Sweden. Tel.: +46 31 786 2590; Fax: +46 31 786 2599; E-mail: lisa.magnusson@cmb.gu.se
3Present address: Astra Tech AB, Mölndal, Sweden
4Present address: Universidad Pablo de Olavide, Seville, Spain
Received 15 January 2009; Accepted 5 June 2009
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 (E
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 E70 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 E70 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 E70. We conclude that ppGpp modulates the levels of free E70 and that this is an integral part of the alarmone's means of regulating a trade-off between growth and maintenance.
Keywords:
- passive regulation,
- ppGpp,
- RNA polymerase,
- stringent control,
- transcriptional trade-off
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