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Nucleic Acids Research, 1975, Vol. 2, No. 7 1053-1072
© 1975

Articles

Inhibitors of protein synthesis V* Irreversible interaction of antibiotics with an initiation complex

C. Coutsogeorgopoulos, J. T. Miller and D. M. Hann

Department of Experimental Therapeutics, Grace Cancer Drug Center, Roswell Park Memorial Institute, New York State Department of Health 666 Elm Street, Buffalo, New York 14263, USA

Received April 15, 1975.

The initiation complex (t-complex) formed in a cell-free system (E. coli) from Ac-Phe-tRNA, poly(U) and washed ribosomes in the presence of initiation factors (ribosomal wash) and GTP, contains the Ac-Phe-tRNA bound quantitatively in a puromycin-reactive state. The t-complex is irreversibly inactivated by spiramycin with respect to its reactivity towards puromycin. The inactivated t-complex retains all of the Ac-Phe-tRNA bound, but it does not react with puromycin (2 x 10–3M) within 32 min at 25°. In the case of another inhibitor of protein synthesis, sparsomycin, the permanently "modified" t-complex not only retains all the bound Ac-Phe-tRNA but it can still react with puromycin. In the continuous presence of sparsomycin (1 x 10–7M) the bound Ac-Phe-tRNA reacts quantitatively at a rate which is one-tenth the rate at which the t-complex reacts with puromycin, at low (6.25 x 10–5 M) or high (2 x 10–3M) concentrations. These results are not in agreement with current views according to which sparsomycin binds to the ribosome reversibly at a single site with a KI in the range of 10–6 10–7M and according to which this site is at the A'-site (puromycin site) of peptidyi transferase.

*Part IV is: Coutsogeorgopoulos, C., Bloch, A., Watanabe, K. A. and Fox, J.J. (1975), J. Med. Chem. (in press).


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