Evolution of the tRNA~(Tyr)/TyrRS aminoacylation systems

摘要

The tRNA identity rules ensuring fidelity of translation are globally conserved throughout evolution except for tyrosyl-tRNA synthetases (TyrRSs) that display species-specific tRNA recognition. This discrimination originates from the presence of a conserved identity pair, G1-C72, located at the top of the acceptor stem of tRNA~(Tyr) from eubacteria that is invariably replaced by an unusual C1-G72 pair in archseal and eubacterial tRNA~(Tyr). In addition to the key role of pair 1-72 in tyrosylation, discriminator base A73, the anticodon triplet and the large variable region (present in eubacterial tRNA~(Tyr) but not found in eukaryal tRNA~(Tyr) contribute to tyrosylation with variable strengths. Crystallographic structures of two tRNA~(Tyr)/TyrRS complexes revealed different interaction modes in accordance with the phylum-specificity. Recent functional studies on the human mitochondrial tRNA~(Tyr)/TyrRS system indicates strong deviations from the canonical tyrosylation rules. These differences are discussed in the light of the present knowledge on TyrRSs.