Basal ppGpp level adjustment shown by new spoT mutants affect steady state growth rates and rrnA ribosomal promoter regulation in Escherichia coli |
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Authors: | Edoardo Sarubbi Kenneth E Rudd and Michael Cashel |
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Institution: | (1) Section of Molecular Regulation, Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, National Institutes of Health, 20892 Bethesda, MD, USA;(2) Present address: Centro Ricerche Lepetit, I-21040 Gerenzano (VA), Italy;(3) NICHD, NIH, Building 6, Room 335, 20892 Bethesda, MD, USA |
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Abstract: | Summary This work describes an approach towards analyzing the regulatory effects of variation of guanosine 3,5-bispyrophosphate (ppGpp) basal levels in Escherichia coli during steady state growth. A series of strains was derived by mutating the spoT gene (which encodes the major cellular ppGppase) so as to obtain systematic increments in ppGpp basal levels. These strains differ genetically at the spoT locus and, in some cases, also at the relA locus because of the severity of spoT mutant alleles. Measurements of ppGpp revealed a ten-fold range of basal levels during growth on minimal medium. The empirical relationship between ppGpp concentration and growth rate is a simple linear inverse correlation. Tandem rrnA ribosomal RNA promoters, present on a multicopy plasmid, are shown to be differentially regulated over this range of basal levels. The upstream P
1 promoter activity shows an inverse exponential relation to ppGpp concentration whereas the downstream P
2 promoter is only weakly affected. We conclude that there are systematic regulatory consequences associated with small changes in ppGpp basal levels during steady state growth that probably are part of a continuum with more dramatic effects observed during the stringent response to amino acid deprivation. |
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Keywords: | ppGpp Growth rate control spoT 3-Aminotriazole |
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