J. Biol. Chem., Vol. 261, Issue 23, 10496-10505, 08, 1986
The translational efficiency of tRNA is a property of the anticodon arm
M Yarus, S Cline, L Raftery, P Wier and D Bradley
We have reciprocally transplanted the anticodon arm sequences of a set of
amber suppressor tRNA genes, using recombinant DNA techniques. By this
means, a very efficient suppressor may be converted to a poor one, and the
poorest tRNA to the efficiency of the best one. In tRNA molecules of normal
2 degrees and 3 degrees structure, the suppressor efficiencies of different
composite tRNAs having the same anticodon arm sequence are approximately
the same. Large numbers of simultaneous changes throughout the rest of the
molecule do not affect the efficiency. Selective nucleotide modification as
a result of varied anticodon arm sequences cannot explain these
efficiencies. Efficiencies are also unlikely to differ because of selective
aminoacylation. Measurement of in vivo tRNA shows, however, that tRNA
levels do vary if the anticodon arm sequence is changed. If tRNA levels are
normalized, the anticodon arm effect on the translational efficiency
remains. Therefore, different anticodon arms, all of normal secondary
structure, are not equivalent in translation. The most efficient sequences
in this series resemble those found in natural tRNAs associated with
similar anticodons, as is proposed in the extended anticodon theory (Yarus,
M. (1982) Science 218, 646-652). These molecules also provide some
information on the specificity of nucleotide modification enzymes and on
determinants of the steady-state tRNA level.