Mode of action of streptolydigin.

Streptolydigin and rifamycin inhibit the catalytic function of ribonucleic acid (RNA) polymerase. Streptolydigin can inhibit polymerization after the reaction has started, whereas rifamycin is effective only if it is preincubated with RNA polymerase prior to the addition of substrates. The same relationships are observed with respect to these two antibiotics if the nucleoside triphosphate-pyrophosphate exchange reaction is used in the assay system. The inhibitory effect of streptolydigin is reversible by further addition of RNA polymerase but not by addition of deoxyribonucleic acid to the assay system.