Transcription termination factor rho mediates simultaneous release of RNA transcripts and DNA template from complexes with Escherichia coli RNA polymerase.

Dissociation of RNA and DNA from Escherichia coli RNA polymerase in transcription complexes prepared with enzyme molecules located within and near a rho-dependent transcription termination region on bacteriophage T7 D111 DNA has been studied using a membrane filter-binding assay. Rho protein with ATP present mediated rapid (half-time approximately 27 s) simultaneous dissociation of about 50% of both RNA and DNA. RNA molecules were preferentially released from enzyme molecules located within the termination region. Rapid release of RNA and DNA depended on a nucleoside triphosphate but did not depend on sigma factor. Pretreatment of complexes with ribonuclease prevented dissociation of DNA. Nearly simultaneous dissociation of both RNA and DNA was also detected after a lag of 3 min when the isolated transcription complexes were incubated with all four ribonucleoside triphosphates in the absence of rho factor. In this case, release presumably occurred at the rho-independent termination site that is 5990 nucleotides downstream from the A1 promoter. Thus, the dissociation of DNA from RNA polymerase at rho-dependent and rho-independent transcription termination sites is coupled with or occurs spontaneously soon after the release of transcripts at both sites.