RNA polymerase: direct evidence for two active sites involved in transcription.

Photoaffinity reagents (3'-azido analogues of 5' ATP and 5' GTP) were used to label two different sites at the catalytic surface of the beta subunit of the E. coli DNA dependent RNA polymerase. These sites are used alternately and successively during consecutive phosphodiester bond formation. This result is consistent with our model of rotational translocation for transcription.