Abstract
Primary transcripts made in vitro on bacteriophage T4 DNA by RNA polymerase isolated from normal or T4-infected Escherichia coli were compared by gel electrophoresis. Bacteriophage-modified RNA polymerase fails to initiate transcription at certain promoters recognized by unmodified enzyme. In the T4 tRNA gene region, only 1 of the 2 promoters is active with the modified RNA polymerase. Reconstitution of separated RNA polymerase components demonstrates that this change in promoter site selection results from the modification of core enzyme and not .sigma. factor.