The effects of bacteriocin JF246, produced by Serratia marcescens, on the incorporation of labeled leucine and thymidine, the synthesis of beta-galactosidase, the active transport of labeled leucine and alpha-methyl-d-glucoside, and the cellular levels of adenosine triphosphate (ATP) in Escherichia coli were studied. This bacteriocin strongly inhibited the incorporation of leucine and thymidine into protein and deoxyribonucleic acid, respectively, as well as the active transport of leucine. The accumulation of alpha-methyl-d-glucoside, which is mediated by a phosphoenolpyruvate-dependent phosphotransferase system, was not markedly inhibited. The level of ATP in bacteriocin-treated cells rapidly fell to 10 to 15% of the control value. However, the kinetics of inhibition of macromolecular synthesis by various levels of bacteriocin was not related to the kinetics of ATP decline.