Characterization and promoter selectivity of Lactobacillus acidophilus RNA polymerase

DNA-dependent RNA polymerase has been purified from gram-positive Lactobacillus acidophilus and found to be composed of 4 protein subunits, alpha, beta, beta', and sigma, with molecular weights of 40,000, 150,000, 135,000, and 45,000 kD, respectively, estimated on the basis of SDS-polyacrylamide gel electrophoresis. The purified enzyme exhibits optimal activity in the presence of Mn2+, while Mg2+ shows only a slight effect. The L. acidophilus enzyme transcribes several Escherichia coli promoters examined so far, such as promoters of trp operon, lacUV5, and bla P3 from pBR322, whereas it lacks the ability to recognize bla P1 and tet P2 promoters from pBR322. Thus, the specificity of L. acidophilus RNA polymerase in recognizing the promoters is somehow different from that of the E. coli enzyme. By means of an in vitro transcription assay system for L. acidophilus RNA polymerase, 2 promoters have been identified in the DNA of an L. acidophilus cryptic plasmid (pRNL5). These promoters possess nucleotide sequences in the -10 region similar to the consensus sequence for the E. coli promoters.