RNA Polymerase and Transcription Factors

Gene expression in bacteria is regulated primarily at the level of transcription. Transcription and its regulation have been studied extensively in several gram-negative bacteria, especially Escherichia coli, but mostly neglected in gram-positive bacteria. The major exception is Bacillus subtilis, which because of its amenability to genetic analysis has served as a paradigm for understanding transcription in gram-positive bacteria. This chapter attempts to provide an overview of the roles of the major families of proteins required for transcription and its regulation in B. subtilis. Emphasis is placed on comparing the roles of these factors in B. subtilis and gram-negative bacteria. The nusA product from E. coli, associates with RNA polymerase after initiation of transcription and remains associated with the elongation complex. The sigma subunit of RNA polymerase determines the specificity of promoter utilization. There are at least 10 different sigma factors in B. subtilis, each of which directs RNA polymerase to a different set of promoters. Two regions in most sigma factors in bacteria probably determine the specificity of promoter utilization by making sequence-specific contacts at two regions of promoters located approximately 10 and 35 bp upstream from the start point of transcription. Examples of the use of altered specificity mutations in sigma factors to determine the role of these factors during sporulation are also described.