5′-triphosphate termini of RNAs made in vivo and in vitro by HeLa and KB cell DNA-dependent RNA polymerases

Abstract

Summary This work shows that the 5′-termini of HeLa and KB cell RNAs contain exclusively purine nucleoside triphosphates with a predominance of GTP. Experiments with actinomycin D, at a concentration which inhibits specifically rRNA synthesis, indicate an extensive decrease of GTP at 5′-ends which means that the major part of nucleolar RNAs, presumably including high molecular weight rRNA precursor, start with GTP. The relative maintenance of ATP at 5′-termini under actinomycin D treatment suggests that an important proportion of nucleoplasmic RNAs is initiated with ATP. These results are supported by further data obtained in vitro with KB cell RNA polymerases I and II.