Affinity labeling of E. coli RNA polymerase with substrate and template analogues

Irradiation of E.coli RNA polymerase at 330–360 nm in the presence of either 4-thiouridine triphosphate or polydeoxy-4-thiothymidylic acid leads to covalent substitution by substrate or template analogue and causes irreversible inactivation of the enzyme. Evidence for specific inactivation was obtained from kinetic experiments. The sites of chemical modification of RNA polymerase were shown to be exclusively the subunits β′ and β.