Changes in the promoter range of RNA polymerase resulting from bacteriophage T4-induced modification of core enzyme

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 T4tRNA gene region, only one of the two 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.