Efficient modification of E. coli RNA polymerase in vitro by the N gene transcription antitermination protein of bacteriophage lambda.

The N gene protein of bacteriophage lambda prevents termination of transcription by E. coli RNA polymerase. We describe here the conditions of a cell-free reaction system in which pure N stimulates net transcription up to tenfold and therefore nearly stoichiometrically modifies transcribing RNA polymerase molecules. The reaction contains micrococcal nuclease-treated S100 extract derived from E. coli and a plasmid template DNA containing the lambda early promoter PL, the N utilization site nutL, and the Rho-dependent terminator tL1. Stimulation by N in this system is specific and biologically relevant since it is absent with vector pBR322 DNA and with extracts derived from E. coli strains bearing the nusA1 and nusE71 mutations known to block N function in vivo. We use the system to provide further evidence that ribosomes are not necessary for N function and to demonstrate the direct involvement in N function of the NusA protein of E. coli.