Reconstitution studies show that rifampicin resistance is determined by the largest polypeptide of Bacillus subtilis RNA polymerase.

A procedure has been developed to separate the subunits of Bacillus subtilis RNA polymerase rapidly and in good yield. The method involved the use of a blue dextran-Sepharose column which bound the beta' subunit. A phosphocellulose column was used to separate the alpha and beta subunits. During purification, the enzyme eluted from the DNA-cellulose column in three separate forms in the order alpha2betabeta'deltaomega1,alpha2betabeta'omega1, and alpha2betabeta'omega1sigma. Subunit reconstitution studies with RNA polymerase subunits from wild type and a rifampicin-resistant mutant indicated that the largest polypeptide was responsible for rifampicin resistance. Thus, this subunit is referred to as beta. The mobility of the subunits in sodium dodecyl sulfate-polyacrylamide gel electrophoresis cannot be used as the sole criterion for designating the functions of the subunits of RNA polymerase.