GENETIC AND TRANSCRIPTIONAL ORGANIZATION OF THE REGION ENCODING THE BETA-SUBUNIT OF BACILLUS-SUBTILIS RNA-POLYMERASE

The gene encoding the beta subunit of Bacillus subtilis RNA polymerase was isolated from a lambda gt11 expression library using an antibody probe. Gene identity was confirmed by the similarity of its predicted product to the Escherichia coli beta subunit and by mapping an alterat ion conferring rifampicin resistance within the conserved rif coding r egion. Including the rif region, four colinear blocks of sequence simi larity were shared between the B. subtilis and E. coli beta subunits. In E. coli, these conserved blocks are separated by three regions that either were not conserved or were entirely absent from the B. subtili s protein. The B. subtilis beta gene was part of a cluster with the or der rplL (encoding ribosomal protein L7/L12), orf23 (encoding a 22,513 -dalton protein that is apparently essential for growth), rpoB (beta), and rpoC (beta'). This organization differs from the corresponding re gion in E. coli by the inclusion of orf23. Experiments using promoter probe vectors and site directed mutagenesis located a major rpoB promo ter overlapping the 3'-coding region of orf23, 250 nucleotides upstrea m from the beta initiation codon. Thus, the B. subtilis rpoB region di ffers from its E. coli counterpart in both genetic and transcriptional organization.