Molecular Pharmacology, Vol 2, 444-453, Copyright © 1966 by the American Society for Pharmacology and Experimental Therapeutics

Inhibition of Protein Synthesis by Polypeptide Antibiotics III. Ribosomal Site of Inhibition

¹ Laboratory of Microbial Genetics and Physiology, St. Jude Children's Research Hospital, and University of Tennessee Medical Units, Memphis, Tennessee 38101

The mechanism by which time antibiotics of the PA 114 complex inhibited protein synthesis in cell-free extracts of bacteria was studied. The antibiotic consists of at least two components belonging to two major groups, A and B. Although each antibiotic of groups A and B was effective individually in inhibiting protein synthesis in vivo, in combination they acted synergistically. PA 114 A inhibited protein synthesis best when messenger RNA was not attached to the ribosome and functioning. If the antibiotic was added after the messenger RNA-aminoacyl-tRNA-ribosome complex had formed and was functioning, inhibition of protein synthesis was decreased. This study showed that PA 114 A inimibited polyuridylic acid-directed binding of phenylalanyl-tRNA to 70 S ribosomes. The antibiotic inhibited ribosome function by specifically destroying the functioning of the 50 S ribosome subunit. PA 114 B acted synergistically to inhibit protein synthesis by enhancing the effect of the A component on the 50 S ribosome. These results suggested that the inhibition of protein synthesis by these antibiotics involved an interaction with a site on the 50 S ribosome subunit of the functional 70 S ribosome required for protein synthesis. This site was perhaps the same as or close to the site at which aminoacyl-tRNA bound.

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ACKNOWLEDGMENTS I wish to thank W. D. Celmer, Chas. Pfizer and Co., Inc., for the PA 114, PA 114 A, and PA 114 B; R. Donovick, Squibb Institute for Medical Research, for the vernamycin A and B ; F. J. Wolf, Merck, Sharp and Dohme, for the streptogramin; and Mrs. R. Tirey for her assistance in some of tue experiments. This investigation was supported by Public Health Service Grant GM-l2359-02 from the Division of General Medical Sciences, by Grant GB-3521 from the National Science Foundation, and by the American Lebanese Syrian Associated Charities (ALSAC).