Promoter selectivity of Escherichia coli RNA polymerase. Purification and properties of holoenzyme containing the heat-shock sigma subunit.

An RNA polymerase holoenzyme containing sigma 32, the heat-shock sigma subunit, has been purified from heat-shocked Escherichia coli cells, and its functional properties including the promoter selectivity have been analyzed using the in vitro mixed transcription system. The holoenzyme correctly recognized a heat-shock promoter for the groE gene and efficiently initiated transcription at the same site as that found in vivo. The enzyme was, however, unable to recognize the promoters which are usually transcribed by the regular holoenzyme (E sigma 70), such as tufB, nusA, supP, lacUV5, araS, rpsA, recA, rplJ, dnaQ, rnh, and trp promoters. On the other hand, the regular holoenzyme did not recognize the groE promoter. These observations altogether indicate that strict difference exists in the promoter selectivity between two molecular species of the RNA polymerase holoenzyme. The groE transcription in vitro was not affected significantly within the temperature range from 32 to 42 degrees C. The two sigma subunits could be replaced in vitro on the same core enzyme, supporting the view that the spectrum of gene expression in E. coli is under a dynamic control by intracellular levels of individual sigma subunits.