Stereochemistry of polymerization by DNA-dependent RNA-polymerase from Escherichia coli: An investigation with a diastereomeric ATP-analogue.

The phosphodiester bond formation by DNA-dependent RNA-polymerase (RNA nucleotidyltransferase, nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) can in principle result in retention, inversion, or racemization of configuration at the alpha-phosphorus of the nucleoside 5'-triphosphate being polymerized. As a first step in elucidating the stereochemistry of this reaction, one diastereomer (A) of adenosine 5'-O-(1-thiotriphosphate) (ATPalphaS) was polymerized with UTP in the presence of poly(dA-dT)-poly(dA-dT). The resulting polymer was enzymatically cleaved to uridine 2',3'-cyclic phosphorothioate which was determined to be the endo-isomer by comparison with an authentic sample. This shows that no reacemization had occurred and that isomer A of ATPalphaS gives a phosphorothioate diester bond with the R-configuration. Whether this represents inversion of retention of configuration awaits elucidation of the absolute configuration of isomer A for ATPalphaS.