Effect of rifamycins and related antibiotics on the deoxyribonucleic acid-dependent ribonucleic acid polymerase of vaccinia virus particles.

A number of compounds related to rifampin which act as expected in the Escherichia coli system have been tested for their ability to inhibit the vaccinia particle deoxyribonucleic acid-dependent ribonucleic acid (RNA) polymerase in vitro. Some compounds are inactive even at concentrations of 500 mug/ml, others are able to produce partial inhibition, and others strongly inhibit the enzyme activity at 150 mug/ml or less. The inhibition, where present, operates immediately but appears to be at least partially reversible. At least one compound which is without effect against bacterial RNA polymerase is a potent inhibitor of the viral RNA polymerase. As the enzyme activity of rifampin-resistant mutants of vaccinia virus is inhibited to the same extent as that of the wild type, the observed in vitro effect on vaccinia virus RNA polymerase is not identical with the in vivo effect specifically directed against a vaccinia-specified protein.