On the probability of a common origin for tRNA and 5S rRNA.

As part of a continuing study on the origin of genetic coding and the process of protein synthesis, we have compared sequences of a large number of transfer RNAs and several 5S ribosomal RNAs using automated routines. Transfer RNAs were found to exhibit a high degree of matching with 5S rRNAs. These matches are considered to be indicative of sequence homology, reflecting common ancestry of the two molecules. Other possible explanations for the matches (convergence, transfection) are discussed and found to be highly implausible. Matches are also found between 5S rRNA and the introns of yeast precursor tRNAs. Many matches extend from before the 3' end to after the 5' end of circularized 5S rRNA sequences. Data is presented which indicates a tandemly duplicated or circular molecule could have served as the precursor to both 5S rRNA and tRNA. A derivative of this molecule may have functioned as a universal translator before the evolution of the highly specialized tRNAs.