In VitroCharacterization of Transcription Termination Factor Rho fromEscherichia coli rho(nusD)Mutants

Escherichia coli nusDstrains are bacteria that carry mutations inrho, the gene for transcription termination factor Rho, that block the growth of phages T4 andλr32. We have identified therhomutation in six independentnusDstrains, 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 theλcromessage as cofactor. At the λ tR1 Rho-dependent terminatorin vitro, all mutant Rho proteins show decreased termination compared with wild-type, and all also terminate withincroat 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.