Mapping of the priming substrate contacts in the active center of Escherichia coli RNA polymerase.

The active center of DNA-dependent RNA polymerase performs the principal biochemical reaction of gene expression. Using cross-linkable substrate analogs and site-directed mutations, two evolutionarily invariant amino acids in the beta subunit of the Escherichia coli enzyme (Lys1065 and His1237) were mapped close to the binding site of the priming substrate of the reaction. Surprisingly, the mutational substitution of these residues (Lys1065----Arg and His1237----Ala) did not inactivate the catalytic function, but inhibited transition from the initiation to the elongation stage of transcription.