Pribnow Box Recognition and Melting by Escherichia coli RNA Polymerase

Abstract

The core RNA polymerases from bacterial and eukaryotic cells, which are homologous in structure and function (Allison et al. 1985; Biggs et al. 1985; Ahearn et al. 1987; Sweetser et al. 1987; Darst et al. 1989, 1991; Schultz et al. 1993; Polyakov et al. 1995), are catalytically active in RNA chain elongation but are incapable of promoter recognition and specific initiation. Promoter-specific transcription initiation requires additional protein factors. In bacteria, specific initiation by RNA polymerase (RNAP) requires a single polypeptide known as a σ factor, which binds to core RNAP to form the holoenzyme (Burgess et al. 1969; Travers and Burgess 1969). One primary σ factor directs the bulk of transcription during exponential growth. Specialized, alternative σ factors direct transcription of specific regulons during unusual physiological or developmental conditions (reviewed in Helmann and Chamberlin 1988; Gross et al. 1992). The primary and most of the alternative σ factors comprise a highly homologous family of proteins (Stragier et al. 1985; Gribskov and Burgess 1986) with four regions of highly conserved amino acid sequence (Fig. 1; reviewed in Lonetto et al. 1992). Based on the results of genetic and biochemical experiments, specific functions have been assigned to some of the conserved regions(summarized in Fig. 1).