Hybridization in vitro of Subunits of the DNA‐Dependent RNA Polymerase from Escherichia coli and Micrococcus luteus

RNA polymerase core enzyme from the gram‐positive bacterium Micrococcus luteus is composed of three different types of subunits, very similar to the equivalent enzyme from the gram‐negative Escherichia coli although the overall net charge and the molecular size of the subunits is different. As in the E. coli enzyme the property of rifampicin resistance resides completely in the second largest subunit p. To investigate the functional correspondence of the subunits, intergeneric polymerase hybrids have been prepared in vitro from the isolated subunits. Active hybrids were obtained from mixtures of subunit α (from M. luteus) with β and β′ (from E. coli), of subunits α and β (from E. coli) with β′ (from M. luteus), of subunit α (from E. coli) with β and β' (from M. luteus), of subunit α and β′ (from M. luteus) with β (from E. coli). Rifampicin resistance and sensitivity of the hybrids containing subunit β from E. coli was solely determined by the resistance and sensitivity respectively of the E. coli RNA polymerase from which subunit β was isolated. The rate of formation of these hybrids is distinctly slower than the reconstitution of the parent E. coli RNA polymerase from subunits. The final activity reached during incubation is different for the various hybrids. All hybrids were able to transcribe natural and synthetic DNA and to catalyse the DNA‐directed synthesis of poly(A), whereas they were inactive in the de novo synthesis of poly(A) · poly(U) and poly(I‐C) · poly(I‐C) in contrast to the reconstituted E. coli enzyme. These results indicate a common structural and functional organization of bacterial RNA polymerases.