Characterization of T7-specific Ribonucleic Acid Polymerase

The response of T7-specific RNA polymerase to a variety of inhibitors of transcription has been studied. T7 RNA synthesis by T7 RNA polymerase is inhibited by actinomycin D, heparin, elevated concentrations of salt and polyr(U). All of these inhibitors block transcription immediately, even after the initiation of RNA synthesis, and hence appear to inhibit T7 RNA polymerase even during RNA chain growth. This is in contrast to transcription by the bacterial RNA polymerase for which RNA chain growth is not sensitive to heparin, elevated salt concentrations, or polyuridylic acid. T7 RNA synthesis by T7 RNA polymerase is not affected by the drugs rifampicin, streptolydigin, and streptovarivin, and is not greatly affected by preincubation of the enzyme with polyr(C), polyr(I), or a variety of heterologous DNAs. Ultraviolet irradiation of T7 DNA blocks its template activity. Such ultraviolet-irradiated T7 DNA serves as an inhibitor of T7 RNA polymerase which appears to inactivate free T7 RNA polymerase, but not T7 RNA polymerase involved in RNA chain growth.