Stimulatory effect of trehalose on formation and activity of Escherichia coli RNA polymerase E sigma38 holoenzyme

The intracellular concentration of trehalose increases in the stationary-phase cells of Escherichia coli. The effects of trehalose on transcription in vitro by E. coli RNA polymerase were compared for two holoenzymes, E sigma70 and E sigma38, which were reconstituted from purified core enzyme and either sigma70 (the major sigma at the exponential growth phase) or sigma38 (the essential sigma at the stationary growth phase), respectively. The optimum trehalose concentration giving maximum transcription by E sigma38 was higher than that by E sigma70. Transcription activation by trehalose was attributed to both increased formation of E sigma38 holoenzyme and increased transcription initiation by E sigma38 from sigma38-dependent promoters. The activation of E sigma38 by trehalose was additive with the transcription enhancement by decreased superhelicity of template DNA prepared from stationary-phase cells. We thus propose that the selective activation of transcription by E sigma38 holoenzyme takes place in the presence of specific conditions and factors present under stress conditions.