Isolation and Characterization of the DNA-dependent RNA Polymerase of Rhizobium leguminosarum 300

The DNA-dependent RNA polymerase isolated from Rhizobium leguminosarum 300 contains the following subunits: β', β, polypeptide A and α (molecular weights 149000, 146000, 93000 and 42000, respectively). Polypeptide A is postulated to be the σ factor of the enzyme. The experimental conditions used for the in vitro assay of the enzyme activity, with plasmid pMB9 as template, included: 40 mM-Tris/HCl (pH 7.9), 150mM-NaCl, 5 mMMgCl2, at 34 °C. The isolated enzyme was shown by electron microscopy to bind specifically to the region of early promoters of DNA of the Escherichia coli bacteriophage T7. Therefore, Rhizobium-specific promoters may have base sequences in common with those of E. coli.