Alteration of ribosomal protein L5 in a thiopeptin-resistant mutant of Escherichia coli

Methylation of basic proteins in ribosomes from wild-type and thiostrepton-resistant strains of Bacillus megaterium and their electrophoretic analysis

Ribosomes, radioactively labelled in vivo with both [1-14C]methionine and [methyl-3H]methionine, have been isolated from both wild-type and thiostrepton-resistant strains of Bacillus megaterium and their constituent proteins separated by two-dimensional gel electrophoresis. Ribosomes from the wild-type strain possess one basic protein that is extensively methylated. In contrast no such protein can be detected in ribosomes from the thiostrepton-resistant strain.

Inhibition by thiopeptin of bacterial protein synthesis

Thiopeptin, a sulfur-containing antibiotic, was found to inhibit protein synthesis in a bacterial ribosomal system. The pretreatment of ribosomal subunits with the antibiotic revealed that thiopeptin may act on the 50 S ribosomal subunit. The elongation of peptide chain on the ribosome is more profoundly blocked by the antibiotic than the initiation of protein synthesis. It was demonstrated that thiopeptin inhibits elongation factor (EF)-Tu-dependent GTP hydrolysis and binding of aminoacyl-tRNA to the ribosome. The peptidyl transferase-catalyzed puromycin reaction is not significantly affected by the antibiotic. Thiopeptin inhibits EF-G-associated GTPase reaction, and translocation of peptidyl-tRNA and mRNA from the acceptor site to the donor site. Protein synthesis in ribosomal systems, obtained from rat liver and rabbit reticulocytes are insensitive to the antibiotic.