Ribosomal complexes Init and preT complexes were prepared according to Zavialov and Ehrenberg [8]. PostT and preTerm complexes were obtained according to Zavialov et al. [9]. In some experiments either [33P]-labeled mRNA [11] or [33P]-tRNAfMet was used for complex preparation. The frac- tion of peptidyl-tRNA in the complexes was more than 80% (for Init, postT and preTerm complexes) or 70% (for preT).