RESUMO
In Fig. 1b of this Article, a U was inadvertently inserted after G15 in the D loop. The original Article has not been corrected.
RESUMO
Ligation of tRNAs with their cognate amino acids, by aminoacyl-tRNA synthetases, establishes the genetic code. Throughout evolution, tRNA(Ala) selection by alanyl-tRNA synthetase (AlaRS) has depended predominantly on a single wobble base pair in the acceptor stem, G3â¢U70, mainly on the kcat level. Here we report the crystal structures of an archaeal AlaRS in complex with tRNA(Ala) with G3â¢U70 and its A3â¢U70 variant. AlaRS interacts with both the minor- and the major-groove sides of G3â¢U70, widening the major groove. The geometry difference between G3â¢U70 and A3â¢U70 is transmitted along the acceptor stem to the 3'-CCA region. Thus, the 3'-CCA region of tRNA(Ala) with G3â¢U70 is oriented to the reactive route that reaches the active site, whereas that of the A3â¢U70 variant is folded back into the non-reactive route. This novel mechanism enables the single wobble pair to dominantly determine the specificity of tRNA selection, by an approximate 100-fold difference in kcat.