[Highly selective affinity labeling of DNA-dependent RNA-polymerase of bacteriophage T7]

T7 phage RNA polymerase was affinity labelled in the presence of its promoter by treatment with an ATP gamma-derivative (a phosphoamide obtained from 4-(N-chloroethyl, N-methyl)aminobenzylamine, or one of esters obtained from 2-methoxy-4-formylphenol, 4-formylphenol, and 2[N-(4-formylphenyl), N-methyl]-aminoethanol) followed by addition of [alpha-32P]GTP. The most efficient labelling took place with the alkylating phosphoamide reagent.