Promoter Selectivity of Escherichia coli RNA Polymerase Eσ70 and Eσ38 Holoenzymes

The functional specificity was compared between two σ factors, σ70 (the major σ at exponentially growing phase) and σ38 (the essential σ at stationary growth phase), of Escherichia coli RNA polymerase. The core enzyme binding affinity of σ38 was less than half the level of σ70 as measured by gel filtration column chromatography or by titrating the concentration of σ 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 Eσ38 than Eσ70. The transcription by Eσ38 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 Eσ38 holoenzyme requires either a specific reaction condition(s) or a specific factor(s) such as template DNA with low superhelical density. The functional specificity was compared between two σ factors, σ70 (the major σ at exponentially growing phase) and σ38 (the essential σ at stationary growth phase), of Escherichia coli RNA polymerase. The core enzyme binding affinity of σ38 was less than half the level of σ70 as measured by gel filtration column chromatography or by titrating the concentration of σ 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 Eσ38 than Eσ70. The transcription by Eσ38 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 Eσ38 holoenzyme requires either a specific reaction condition(s) or a specific factor(s) such as template DNA with low superhelical density.