ACTINOMYCIN: CORRELATION OF STRUCTURE AND FUNCTION OF ITS COMPLEXES WITH PURINES AND DNA.

Actinomycin inhibits strand separation of helical DNA at concentrations corresponding to those which inhibit DNA polymerase activity in vitro. This report proposes first that actinomycin affects DNA polymerase indirectly by way of the changed physical properties of the template and that it functions in the major groove of helical DNA; second, that RNA polymerase functioning in the minor groove is subject to direct steric inhibition by bound actinomycin; and third, that the reaction of actinomycin with free purines is unrelated to its reaction with DNA.