V.Z.Volloch1, S.Rits2 and L.Tumerman*

Nucleoside triphosphate phosphohydrolase (NTPase) activity was found in a preparation of E. Coli RNA polymerase. This enzymatic activity is capa-able of hydrolysing all four ribonucleoside triphosphates to the nucleoside diphosphates. However, during in vitro RNA synthesis directed by poly(dC) or poly(dT), only the non-complementary nucleoside triphosphate of the same heterocyclic class was hydrolysed. No incorporation of the non-comple-mentary precursor into RNA could be detected in these experiments. When an-other RNA polymerase preparation, devoid of NTPase activity, was employed, there was no hydrolysis of any nucleoside triphosphate and significant in-corporation of non-complemtary precursor into RNA was observed. These observations lead us to the conclusion that NTPase, acting in con-Junction with RNA polymerase, has the function of correcting errors in transcription