GENETIC-CODE ORIGINS - TRANSFER-RNAS OLDER THAN THEIR SYNTHETASES

We present a phylogenetic analysis to determine whether a given tRNA m olecule was established in evolution before its cognate aminoacyl-tRNA synthetase. The earlier appearance of tRNA versus their metabolically related enzymes is a prediction of the RNA world theory, but the avai lable synthetase and tRNA sequences previously had not allowed a forma l comparison of their relative time of appearance. Using data recently obtained from the emerging genome projects, our analysis points to th e extant forms of lysyl-tRNA synthetase being preceded in evolution by the establishment of the identity of lysine tRNA.