Figure 1.

Model 40S (1 and 2) and 80S (3 and 4) ribosomal complexes with the nonaribonucleotide mRNA analog bearing two spin labels, one at the 5′-terminal phosphate and another at the adenosine in sixth position. P and A are ribosomal tRNA binding sites. In complexes 1 and 3 the mRNA analog is implicated in codon-anticodon interaction with cognate tRNA^Phe at the P site, and in complexes 2 and 4 codon-anticodon interactions occur at both the A and the P sites. At the bottom, chemical structures of derivatized adenosine and 5′-terminal phosphate of the mRNA analog are shown.