Tetracycline can inhibit tRNA binding to the ribosomal P site as well as to the A site

Abstract

A and P sites of Escherichia coli ribosomes were titrated with AcPhe‐tRNAPhe, in the absence or presence of tetracycline. The P‐site location of the bound AcPhe‐tRNA was assessed by means of a quantitative puromycin reaction. The results demonstrate that, in agreement with the generally held view, tetracycline exclusively inhibits the A‐site binding, if the statistical number of bound acyl‐tRNA molecules per ribosome does not exceed about 0.5. However, above this value the P site becomes sensitive to tetracycline as well. It follows that the tightly coupled 70S ribosomes used in functional studies appear to be functionally heterogeneous, i. e. those P sites which cannot be affected by tetracycline are preferentially occupied by AcPhe‐tRNA, whereas higher concentrations of this tRNA species are required to fill tetracycline‐sensitive P sites. Furthermore, the results imply that under tRNA saturation conditions the tetracycline inhibition cannot be used as an indicator for the site location of bound tRNA. Copyright © 1986, Wiley Blackwell. All rights reserved