Inhibition of protein synthesis in reticulocytes by antibiotics. II. The site of action of cycloheximide, streptovitacin A and pactamycin.

The inhibition of protein synthesis by cycloheximide, streptovitacin A and pactamycin has been studied. The inhibition by pactamycin has been located in the ribosomal fraction. The ribosomes of reticulocytes incubated with pactamycin are not stimulated by polyuridylic acid in a cell-free system. Thus pactamycin appears to alter a ribosomal site which is involved in the interaction between messenger RNA, transfer RNA, and ribosome, and which is essential to protein synthesis. Cycloheximide and streptovitacin A specifically inhibit the formation of the peptide bond catalyzed by a 100 000 × g supernatant factor. This has been shown by experiments with puromycin which indicate that cycloheximide and streptovitacin A inhibit the release, caused by puromycin, of incomplete peptide chains from polysomes. Since the release of peptide chains by puromycin requires the formation of a peptide bond, the supernatant factor inhibited by cycloheximide and streptovitacin A has been tentatively identified with the enzyme peptide synthetase.