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Abstract
The functional specificity was compared between two sigma factors, sigma 70 (the major sigma at exponentially growing phase) and sigma 38 (the essential sigma at stationary growth phase), of Escherichia coli RNA polymerase. The core enzyme binding affinity of sigma 38 was less than half the level of sigma 70 as measured by gel filtration column chromatography or by titrating the concentration of sigma required for the maximum transcription in the presence of a fixed amount of core enzyme. In addition, the holoenzyme concentration required for the maximum transcription of a fixed amount of templates was higher for E sigma 38 than E sigma 70. The transcription by E sigma 38 was, however, enhanced with the use of templates with low superhelical density, in good agreement with the decrease in DNA superhelicity in the stationary growth phase. We thus propose that the selective transcription of stationary-specific genes by E sigma 38 holoenzyme requires either a specific reaction condition(s) or a specific factor(s) such as template DNA with low superhelical density.
Highlights
The functional specificity was compared between two factors, 70 and 38, of Escherichia coli RNA polymerase
The results show that the selectivity for stationary phase-specific promoters by E38 increases concomitantly with the decrease in DNA superhelicity and that the effects of decreased DNA superhelicity and high potassium glutamate concentrations are additive in enhancing the selectivity for E38
Difference in the Core Enzyme Binding Activity between Two Factors—Both 70 and 38 were overproduced in E. coli and purified to apparent homogeneity as determined by Coomassie Brilliant Blue staining of the proteins separated by PAGE
Summary
The functional specificity was compared between two factors, 70 (the major at exponentially growing phase) and 38 (the essential at stationary growth phase), of Escherichia coli RNA polymerase. The total number of genes on the E. coli genome is estimated to be about 4,000, which is in good agreement with the number estimated from the DNA sequence (up to now, more than 60% has been sequenced) These considerations raise a possibility that competition must take place between promoters for binding a small number of RNA polymerase molecules. We found that the osmo-regulated genes, osmB and osmY, are transcribed preferentially by E38 only in the presence of high concentrations of potassium glutamate (or acetate) [16] This finding raises a possibility that each stationary-specific promoter carries a specific sequence that is recognized by E38 under a specific reaction condition and suggests that the promoter sequences recognized by E38 differ between gene groups with different requirements. The results show that the selectivity for stationary phase-specific promoters by E38 increases concomitantly with the decrease in DNA superhelicity and that the effects of decreased DNA superhelicity and high potassium glutamate concentrations are additive in enhancing the selectivity for E38
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