The idea of a polysemous codon also differs from the activities of variants mutated at position 37 with A or G using the variants with A at the discriminator position 'near-cognate' concept proposed by Schultz and Yarus (1994) . They claimed that ambiguous decoding may occur which effectively elevates leucylation activity. In our work, we utilized serine tRNA with a modified nucleoside as a consequence of an irregular codon-anticodon interaction induced by the 27-43 base pair at the anticodon and with G at the discriminator position as a substrate for LeuRS, because the T7 transcript of tRNA Ser CAG showed stem of the tRNA, resulting in a genetic code change transition state. The polysemous codon found in our study no activity for leucylation. Our experiments using microsurgery methods indicated that m 1 G is of great importance is caused by the tRNA aminoacylation process of tRNA with codon-anticodon interaction proceeding precisely in in leucylation, despite the fact that the presence of G at the discriminator position is unsuitable for the recognition the conventional manner . Furthermore, since the hypothesis of Schultz and Yarus is based of LeuRS. Some modified nucleotides in tRNA are known to be involved in recoginition of some synthetases (Muramatsu et al., 1988) . Pütz et al. (1994) showed that m 1 G at position 37 of yeast tRNA Asp is one of the negative determinants for arginyl-tRNA synthetase.