Atomic mutagenesis at the ribosomal decoding site.

Ribosomal decoding is an essential process in every living cell. During protein synthesis the 30S ribosomal subunit needs to accomplish binding and accurate decoding of mRNAs. From mutational studies and high-resolution crystal structures nucleotides G530, A1492 and A1493 of the 16S rRNA came into focus as important elements for the decoding process. Recent crystallographic data challenged the so far accepted model for the decoding mechanism. To biochemically investigate decoding in greater detail we applied an in vitro reconstitution approach to modulate single chemical groups at A1492 and A1493. The modified ribosomes were subsequently tested for their ability to efficiently decode the mRNA. Unexpectedly, the ribosome was rather tolerant toward modifications of single groups either at the base or at the sugar moiety in terms of translation activity. Concerning translation fidelity, the elimination of single chemical groups involved in a hydrogen bonding network between the tRNA, mRNA and rRNA did not change the accuracy of the ribosome. These results indicate that the contribution of those chemical groups and the formed hydrogen bonds are not crucial for ribosomal decoding.