The properties of ATP-analogs in initiation of RNA synthesis catalyzed by RNA polymerase from E coli.

Various base and sugar modified derivatives of ATP and UTP were used as substrate analogs for the steady state initiation reaction ATP+UTP=pppApU and the single step addition reaction ApC+ATP=ApCpA. These reactions were carried out by E. coli RNA polymerase on T7 DNA in the presence of rifampicin. The steady state kinetic parameters of the analogs, either as substrates or inhibitors, were determined. On the basis of the obtained results it is concluded that purine NTP s in initiation require anti-conformation about the glycosidic bonds as well as gauche-gauche conformation of the C(4')-C(5') bonds. The latter conformation is also a prerequisite for substrates in elongation, whereas strict anti-conformation of glycosidic bonds is not.