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 β 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.