MECHANISM OF CHLORAMPHENICOL-INDUCED CHANGES IN THE PHOTOINDUCED AFFINITY LABELING OF ESCHERICHIA-COLI RIBOSOMES BY PUROMYCIN - EVIDENCE FOR PUROMYCIN AND CHLORAMPHENICOL SITES ON THE 30S-SUBUNIT

Chloramphenicol has been shown to cause a major change in the ribosomal protein labeling pattern when Escherichia coli ribosomes are photolyzed in the presence of radioactive puromycin. In the absence of chloramphenicol, the major labeled protein is L23, while in its presence S14 becomes the major labeled protein [Grant, P. G., Strycharz, W. A., Jaynes, E. N„ Jr., & Cooperman, B. S. (1979) Biochemistry (preceding paper in this issue)]. This paper reports a detailed investigation of this change, which has allowed the following conclusions to be drawn. (1) The labeling of S14 by puromycin proceeds from a puromycin binding site. (2) The stimulation of S14 labeling by chloramphenicol requires a specific chloramphenicol binding site. (3) Both of the above binding sites are located on the 30S subunit. (4) The stimulation of S14 labeling occurs as a result of a chloramphenicol-dependent light-induced alteration of the 30S subunit. Overall, our results and those obtained in related studies provide evidence that there are binding sites for both chloramphenicol and puromycin on both the 50S and 30S subunits and that the sites on each of the subunits are close to one another. They also provide a clear demonstration of the importance of examining labeling patterns as a function of light fluence in photoincorporation experiments. The possible significance of the previously unsuspected puromycin and chloramphenicol sites on the 30S subunit is discussed. © 1979, American Chemical Society. All rights reserved.