The inhibitory activities of a novel antibiotic compound have been investigated. A synthetic version of the natural product TAN-1057A was examined for its effects on translation and ribosomal subunit formation. The antibiotic at 6 mug/ml reduced the growth rate of wild-type Staphylococcus aureus cells by 50%. The IC50 for inhibition of protein synthesis in these cells was 4.5 mug/ml. Pulse and chase labeling kinetics showed a strong inhibitory effect on 50S ribosomal subunit formation as well. The IC50 for this process was 9 mug/ml, indicating an equivalent inhibitory effect of the antibiotic on translation and 50S synthesis. The post-antibiotic effect of the drug was investigated. Protein synthesis resumed rapidly after removal of the drug from cells, but full recovery of the normal 50S subunit complement in treated cells required 1.5 h. The dual inhibitory effects of this compound are compared with other antimicrobial agents having similar effects on cell growth.