Recognition sites on tRNA. Circles represent nucleotides, and the sizes of the circles are proportional to the frequency with which they are used as recognition sites by aminoacyl-tRNA synthetases. The numbers indicate the positions of the nucleotides in the base sequence, beginning from the 5′ end of the tRNA molecule.

[Information from M. Ibba, and D. Söll, Annu. Rev. Biochem. 69:617–650, 1981, p. 636.]