Animal DNA‐Dependent RNA Polymerases

Abstract

We have analyzed the parameters which influence the transcription in vitro of the allomorphic forms of Simian virus 40 (SV 40) DNA by mammalian RNA polymerases AI and B. Comparative studies with Escherichia coli core and holoenzyme RNA polymerase are also reported. Our studies demonstrate that the nature of the divalent cation present in the reaction, the ionic strength, and the physical configuration of SV40 DNA have marked effects on the template efficiency of this DNA for mammalian RNA polymerases. It was found that the transcription of superhelical SV40 DNA form I was almost completely Mn2+‐dependent, irrespective of the enzyme type. Under all incubation conditions, the open circular form II and particularly the linear form III were poorly transcribed by AI and B RNA polymerases, suggesting that both enzyme have great difficulty in initiating RNA synthesis on well base‐paired intact double‐stranded DNAs. The effects of rifamycin AF/013 and of spermine on RNA synthesis catalysed by the mammalian enzymes on SV40 DNA were also analyzed. Most of our results can be explained in the light of the recent discovery of the existence, in superhelical DNAs, of an alteration of the double helix which could be magnified by the presence of Mn2+.