DNA-dependent single-step addition reactions catalyzed by Escherichia coli RNA polymerase.

The addition of a single nucleotide to a short oligonucleotide, catalyzed by RNA polymerase (nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) in the presence of synthetic DNA templates, has been studied. The reactions A-U + ATP leads to A-U-A and U-A + UTP leads to U-A-U occur in the presence of poly[d(A-T)], while the reactions G-C + GTP leads to G-C-G and C-G + CTP leads to C-G-C take place in the presence of poly[d(I-C)]. These reactions proceed with a turnover of enzyme. The products U-A-U and C-G-C are formed rapidly, while A-U-A and G-C-G are formed much more slowly. Another poly[d(A-T)]-dependent reaction, which occurs with a turnover of enzyme, is U-A-U + ATP leads to U-A-U-A. All of these reactions are only partially inhibited by rifampicin. ATP can be replaced by 3'-deoxyadenosine 5'-triphosphate in the reactions A-U + ATP leads to A-U-A and U-A-U + ATP leads to U-A-U-A, though the rate of formation of the products becomes somewhat slower. The reactions involving 3'-deoxyadenosine 5'-triphosphate are almost completely inhibited by rifampicin, indicating that the 3'-hydroxyl group is necessary for these reactions to occur in the presence of rifampicin.