Inhibition of Qβ RNA 70S ribosome initiation complex formation by an oligonucleotide complementary to the 3′ terminal region of E. coli 16S ribosomal RNA

Abstract

IT has been proposed that a key event in the recognition of a prokaryotic protein initiation site by the ribosome is the interaction between the 3′-terminal sequence of the 16S rRNA and a purine-rich sequence preceding the initiator triplet by three to nine nucleotides^1,2 This hypothesis predicts that if the 3′-terminal region of the 16S rRNA were blocked, binding of the ribosome to the initiator region of an mRNA should be diminished or prevented, while binding to the trinucleotide A-U-G should not be affected We have shown that the oligonucleotide A-G-A-G-G-A-G-G-U_OH (P-2a), eight bases of which are complementary to the sequence A-C-C-U-C-C-U-U-A_OH at the 3′-termmal region of 16S rRNA (ΔG = −16.9 kcal mol⁻¹ calculated as described in Table 1), binds tightly to the 30S ribosome and is released as a complex with the 3′-terminal 49-mer of 16S rRNA after digestion with cloacin DF13 (ref. 3). We report here that this oligonucleotide either strongly inhibits Qβ RNA binding to 70S ribosomes or decreases the stability of the initiation complex formed in its presence As we found that the formation of complexes of pA-U-G and 70S ribosomes was, not inhibited by the oligonucleotide, we conclude that inhibition (or destabilisation) of Qβ RNA binding is not due to an effect on the interaction between fMet-tRNA and the initiation triplet or on the association of the 30S and 50S ribosome subunits.