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On the mechanism of interaction of N-acetylphenylalanyl-tRNAPhe with ribosomes of Escherichia coli: effect of antibiotics and Tp psi pCpGp.

The tetranucleotide Tp psi pCpGp acts as a specific inhibitor of the rate of AcPhe-tRNAPhe binding in the ribosomal P site. This effect is observed both in the presence and in the absence of poly(U). In the absence of poly(U) antibiotics tetracycline and puromycin also decrease the rate of AcPhe-tRNAPhe binding. Some inhibition by tetracycline is observed with poly(U). All these inhibitors are known to be ligands of the ribosomal A site, and their influence on the P site binding can be most naturally explained by the suggestion that AcPhe-tRNAPhe enters the ribosome via the A site, forms there an intermediate complex, and spontaneous translocation into the P site follows. In the presence of poly(U) arguments in favour of this hypothesis are much weaker, but the same sequence of events is possible.