Divergent adaptation of tRNA recognition by Methanococcus jannaschii prolyl-tRNA synthetase

Analysis of prolyl-tRNA synthetase (ProRS) across all three taxonomic domai ns (Eubacteria, Eucarya, and Archaea) reveals that the sequences are divide d into two distinct groups. Recent studies show that Escherichia coti ProRS , a member of the "prokaryotic-like" group, recognizes specific tRNA bases at both the acceptor and anticodon ends, whereas human ProRS, a member of t he "eukaryotic-like" group, recognizes nucleotide bases primarily in the an ticodon, The archaeal Methanococcus jannaschii ProRS is a member of the euk aryotic-like group, although its tRNA(Pro) possesses prokaryotic features i n the acceptor stem, We show here that, in some respects, recognition of tR NA(Pro) by M. jannaschii ProRS parallels that of human, with a strong empha sis on the anticodon and only weak recognition of the acceptor stem. Howeve r, our data also indicate differences in the details of the anticodon recog nition between these two eukaryotic-like synthetases. Although the human en zyme places a stronger emphasis on G35, the M. jannaschii enzyme places a s tronger emphasis on G36, a feature that is shared by E. coli ProRS. These r esults, interpreted in the context of an extensive sequence alignment., pro vide evidence of divergent adaptation by M. jannaschii ProRS; recognition o f the tRNA acceptor end is eukaryotic-like, whereas the details of the anti codon recognition are prokaryotic-like, This divergence may be a reflection of the unusual dual function of this enzyme, which catalyzes specific amin oacylation with proline as well as with cysteine.