Evolution of E. coli tRNA(Trp).

Earlier studies (1) have shown there are direct correlations between the hydrophobicity ranking of most amino acids and their anticodonic nucleotides. However, four anticodonic assignments, i.e. those for Trp, Tyr, Ile and the XGA anticodons for Ser, did not correlate. It was our proposal that this failure to correlate was due to the fact that these assignments were made late, relative to the bulk of the assignments, in evolution through the mutation of existing tRNAs. We have shown (2) that E. coli tRNA(Ile 1) and tRNA(Ile 2) were likely derived from tRNA(Val 1) and tRNA(Lys) respectively and E. coli tRNA(Tyr) was possibly derived from E. coli 5s rRNA or a common precursor with 5s rRNA (3). The fact that quite high homologies were observed in these comparisons is consistent with the late evolution of the tRNAs in question. We now examine the evolution of E. coli tRNA(Trp) by comparing its homology with other E. coli tRNAs. The data suggest a possible evolutionary relationship with E. coli tRNA(Gly) or tRNA(Arg). The data support the idea of the late assignment of anticodons to Trp.