RNA polymerase binding sites in λp lac 5 DNA

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Abstract
The in vitro binding of the Escherichia coli RNA polymerase (nucleosidetriphosphate:RNA nucleotidyltransferase; EC 2.7.7.6) to fragments of λp lac 5 DNA generated by restriction endonucleases Hin dII and Hin dIII has been studied by a filter binding technique. The results are consistent with RNA polymerase binding at p R ′, the INT promoter ( p I ), several sites in the b2 region, the mis promoter, the oop promoter (or p O ), and p rm . Binding was also observed on some fragments that are not known to contain active promoters, including the fragment from the c III- t L region. Some of these binding reactions might also be explained by interaction of RNA polymerase with termination sites. Additional polymerase binding sites have been detected by examining which Hin dII and Hin dIII sites were not cleaved when digestion was performed after RNA polymerase had been bound to the DNA. This technique revealed polymerase binding at p L , at p R , at a site between R and cos , and at a site at the junction of the γ and c III- t L fragments. A comparison of the location of polymerase binding fragments with the partial denaturation map of the λ genome indicates that RNA polymerase binding sites are located within A-T rich regions. It is suggested that RNA polymerase binding is a function both of specific sequences (where recognition occurs) and of the base composition of the surrounding regions (which affects the stability of the helix at the specific site).