In Vitro Studies of RNA/DNA/RNA Polymerase Complexes
Meissner, Paul Scott
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Recent studies with the biosynthetic DNA template poIy [ d ( A - T ) ] poIy [ d ( A - T ) ) have shown that E.Coli DNA-dependent RNA polymerase catalyzes the reactions: UpA + UTP →UpApU and A P U + A T P → A pUpA at different rates (Sylvester, 1980). ApUpA is formed in approximately 1:1 stoichiometry with the amount of enzyme present despite an excess of substrates, yet UpApU is formed catalytically. Addition of the drug rifampicin greatly stimulates ApUpA formation yet it partially inhibits UpApU synthesis. Using the biosynthetic DNA template poly[d(A-C)]· poly [ d ( T -G ) ]. similar results were obtained for the reactions: GpU + GTP → GpUpG and UpG + UTP → UpGpU. GpUpG behaves like ApUpA and UpGpU behaves like UpApU. On the basis of these results, it appears that trinucleoside diphosphates of the structure (Purine)p(Pyrimidine)p(Purine) form stable DNA- RNA· RNA polymerase complexes upon formation of the first phosphodiester bond, yet those with the structure (Pyrimidine)p(Purine)p(Pyrimidine) are unable to form stable complexes.