Characterization of a novel translational inhibitor from Leishmania mexicana promastigotes.

An inhibitory activity blocking protein synthesis elongation in several eukaryotic systems has been detected in Leishmania mexicana extracts. This factor, which competes with aminoacylation of tRNA and also affects the subsequent polymerization step, is a strong inhibitor of polypeptide synthesis induced by poly U in wheat-germ extracts or by endogenous mRNAs in rat liver cell-free systems. The purified translational inhibitor has shown to be essentially free of proteins.

Inhibition of in vivo transcription by actinomycin D treatment of ethylenediaminetetraacetic acid-permeabilized Escherichia coli: effects on bacteriophage proliferation.

Rifampicin, which is able to block DNA-dependent RNA synthesis, has been widely used to selectively inhibit host protein synthesis in RNA bacteriophage-infected Escherichia coli without affecting the viral specific protein synthesis. However, in many cases it is necessary to increase rifampicin levels to 200 micrograms/ml in order to obtain an almost complete suppression of bacterial protein synthesis, and these high antibiotic concentrations cause at the same time a strong inhibition of phage proliferation resulting in a 50- to 100-fold reduction of phage yields. We have partially avoided this difficulty by using actinomycin D after permeabilization of bacteria by a brief incubation with EDTA.

Polyamines modulate streptomycin-induced mistranslation in Escherichia coli.

The effects of intracellular levels of polyamines on both the in vivo inhibition of protein synthesis and the decrease of translation accuracy induced by streptomycin have been studied in polyamine-auxotrophic strains of Escherichia coli infected with the MS2 bacteriophage. The amount of viral coat protein formed was strongly reduced upon addition of increasing concentrations of streptomycin to polyamine-supplemented bacteria. In contrast, the antibiotic almost did not inhibit coat protein synthesis in polyamine-starved cells.