In vitro characterization of transcription termination factor Rho from Escherichia coli rho(nusD) mutants

Escherichia coli nusD strains are bacteria that carry mutations in rho, the gene for transcription termination factor Rho, that block the growth of phages T4 and lambdar32. We have identified the rho mutation in six independent nusD strains, and although five of the strains have different mutations, with one exception the mutations are in the proposed RNA-binding domain of Rho. We overexpressed, purified, and characterized the five different mutant Rho proteins. All show substantial RNA-dependent ATPase activity with several homoribopolymers or the lambda cro message as cofactor. At the lambda tR1 Rho-dependent terminator in vitro, all mutant Rho proteins show decreased termination compared with wild-type, and all also terminate within cro at a new terminator, tRE, with endpoints 5' to tR1 at 170, 200, 245 and 260 nucleotides 3' from the transcription start. The mutant Rho proteins are proposed to interfere with bacteriophage T4 growth through indirect effects on host gene expression.