Transcription of the Escherichia coli rrnB P1 promoter by the heat shock RNA polymerase (Eσ32) in vitro

Abstract

The P1 promoters of the seven Escherichia coli rRNA operons contain recognition sequences for the RNA polymerase (RNAP) holoenzyme containing sigma 70 (Eσ70), which has been shown to interact with and initiate transcription from rrn P1 promoters in vivo and in vitro. The rrn P1 promoters also contain putative recognition elements for Eσ32, the RNAP holoenzyme responsible for the transcription of heat shock genes. Using in vitro transcription assays with purified RNAP holoenzyme, we show that Eσ32 is able to transcribe from the rrnB P1 promoter. Antibodies specific to σ70 eliminate transcription of rrnB P1 by Eσ70 but have no effect on Eσ32-directed transcription. Physical characterization of the Eσ32- rrnB P1 complex shows that there are differences in the interactions made by Eσ70 and Eσ32 with the promoter. Eσ32 responds to both Fis-mediated and factor-independent upstream activation, two systems shown previously to stimulate rrnB P1 transcription by Eσ70. We find that Eσ32 is not required for two major control systems known to regulate rRNA transcription initiation at normal temperatures in vivo, stringent control and growth rate- dependent control. On the basis of the well-characterized role of Eσ32 in transcription from heat shock promoters in vivo, we suggest that Eσ32- directed transcription of rRNA promoters might play a role in ribosome synthesis at high temperatures.