Peptide chain termination. VII. The ribosomal and release factor requirements for peptide release.

Release factors participate in release of fMet from fMet-tRNA . AUG . ribosome intermediates upon binding to ribosomes. This release requires R factor and occurs in the absence of terminator codon in reactions containing 20 per cent ethanol. Release occurs only when both 30S and 50S ribosomal subunits are present and when fMet-tRNA is located in the ribosomal P site. Release factor-dependent deacylation of fMet-tRNA is inhibited by sparsomycin, amicetin, lincocin, and chloramphenicol, antibiotics which have little effect on binding of R factor to ribosomes. The possible role of peptidyl transferase in the release reaction is discussed.