Effect of the anticodon loop size of yeast alanyl tRNA on its biological activity

Three analogs of yeast alanyl tRNA with anticodon loops of different sizes, tRNA75 (no G35 and 5′-terminal phosphate), tRNA77 (one more C between G35 and C36, no 5′-terminal phosphate), and ptRNA79 (with Cm 1Iψ between G35 and C36), were synthesized. In comparison with the reconstituted natural yeast tRNA, the charging activities of the three analogs were 90% (tRNA75), 94.7% (tRNA77), and 104% (ptRNA79). These results supported the conclusion (Yang De-ping and Wang De-bao (T. P. Wang) (1983) Acta Biochim. Biophys. Sin. 15, 83–90) that the anticodon loop of yeast alanyl tRNA was not involved in the interaction between alanyl-tRNA synthetase from rat liver and yeast alanyl tRNA. In contrast, in the rabbit reticulocyte lysate system, the incorporation of alanine in the charged analogs was 0% (tRNA75 and ptRNA79) and 100% (tRNA77). There were significant differences between the incorporation activities of analogs and those of the reconstituted molecule. The reason for these differences in discussed.