[Effect of actinomycin D on purified DNA-dependent RNA polymerases from normal and neoplastic tissues]

The effect of low concentrations of actinomycin D was investigated, using two forms of DNA-dependent RNA polymerase (A and B) purified from normal tissues and experimental tumours, in the presence either of Mn2+ or Mg2+, and homologous DNA. The A enzyme activity was strongly inhibited by the antibiotic in presence of Mg2+ and much less in presence of Mn2+. The B enzyme activity was almost suppressed in presence of both cations. The results here reported provide support that the actinomycin D induce a cellular damage of the same extent in normal and tumour tissues.