| Abstract: | Photolysis of [3H]tetracycline in the presence of Escherichia coli ribosomes results in an approximately 1:1 ratio of labelling ribosomal proteins and RNAs. In this work we characterize crosslinks to both 16S and 23S RNAs. Previously, the main target of photoincorporation of [3H]tetracycline into ribosomal proteins was shown to be S7, which is also part of the one strong binding site of tetracycline on the 30S subunit. The crosslinks on 23S RNA map exclusively to the central loop of domain V (G2505, G2576 and G2608) which is part of the peptidyl transferase region. However, experiments performed with chimeric ribosomal subunits demonstrate that peptidyltransferase activity is not affected by tetracycline crosslinked solely to the 50S subunits. Three different positions are labelled on the 16S RNA, G693, G1300 and G1338. The positions of these crosslinked nucleotides correlate well with footprints on the 16S RNA produced either by tRNA or the protein S7. This suggests that the nucleotides are labelled by tetracycline bound to the strong binding site on the 30S subunit. In addition, our results demonstrate that the well known inhibition of tRNA binding to the A-site is solely due to tetracycline crosslinked to 30S subunits and furthermore suggest that interactions of the antibiotic with 16S RNA might be involved in its mode of action. |
