The translocation inhibitor tuberactinomycin binds to nucleic acids and blocks the in vitro assembly of 50S subunits

Binding studies were performed with a [14C]-labelled derivative of viomycin, tuberactinomycin 0 (TUM O). TUM O bound to 30S and 50S subunits. The binding component was the RNA, since ribosomal proteins did not bind the drug. Other RNAs such as tRNA, phage RNA (MS2), and homopolynucleotides also bound the drug. Striking differences in the binding capacity of the various homopolynucleotides were found. Poly(U) bound strongly, poly(G) and poly(C) bound intermediately, whereas poly(A) showed a very low binding. DNA also bound TUM O, although with native DNA the binding was only weak. Finally the effects of viomycin on the assembly in vitro of the 50S subunit from E. coli were tested. A very strong inhibition was found: when the reconstitution was performed at 0.5 x 10(-6) M viomycin the particles formed sedimented at about 50S, but showed a residual activity of less than 10%. The inhibitory power of viomycin with respect to the in vitro assembly is more pronounced than that found in in vitro systems for protein synthesis.