Based on the calculated CAI values, 5% of the total genes with extremely high and low CAI values were regarded as the high and the low datasets, respectively. Then we compared the codon usage of the high dataset to the low dataset. Table 2 shows that 14 codons that code 13 amino acids were apparently used at a high level, and can be determined as translational optimal codons. Out of the 14 optimal codons, 5 were ended with G, 1 with C and 8 with T.