Photochemical cross-linking studies on the interaction of Escherichia coli RNA polymerase with T7 DNA

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Abstract
The subunits of E. coli RNA polymerase which are in close contact with the T7 phage DNA template were identified using photochemical cross-linking. In nonspecific T7 DNA-enzyme complexes which occur in all regions of the DNA, subunits .sigma., .beta. and .beta.'' were cross-linked to the DNA. In specific binary complexes which presumably occur at promoter sites, and in the initiation complex (holoenzyme + T7 DNA + initiator dinucleotides + three nucleoside triphosphates), only .sigma. and .beta. were cross-linked to DNA, while cross-linking of .beta.'' could not be demonstrated. These results do not support the idea that .alpha. subunits are involved in the enzyme-template interaction, raise the possibility that the .sigma. subunit participates directly in promoter recognition even though isolated .sigma. does not bind to DNA, and indicate different modes of interaction between RNA polymerase and DNA in nonspecific and specific complexes. These findings are relevant to the mechanism by which RNA polymerase carries out selective transcription.