A plausible mechanism by which LeuRS could recog-and Sharp, 1992; Sugiyama et al., 1995; T.Suzuki, personal observations) . During the course of the change in the nize cognate leucine and serine tRNAs specific for codon CUG is illustrated in Figure 6 . LeuRS contacts and genetic code, the genome should pass through a state group 2 (Ohama et al., 1993) . Fourth, the phylogenetic dextrose) and minimal medium SD [0.67% yeast nitrogen base without tree of these species and relatives constructed by using amino acids (Difco) and 2% dextrose] supplied with 24 mg/ml uracil were used for the cultivation of yeast cells.