Acetylated amino acids attached to these tRNAs were A change from G to U at position 33 apparently enhanced deacylated by alkaline treatment and analyzed by TLC. the translation activity 2.5-fold, although their decoding As shown in Figure 4C , acetylserine was observed as a properties did not change at all (data not shown). We thus major amino acid derivative in both tRNA Ser CAGs, but consider that G33 serves as a modulator of leucylation of acetylleucine was detected only in the C.zeylanoides tRNA Ser CAG, despite a slight disadvantage in transla-tRNA Ser CAG; the acetylserine and acetylleucine spots were identified as described previously (Suzuki et al., tion activity. 1996) . The radioactivities remaining on the origins probably came from the direct acetylation of some nucleotides in the tRNAs, as discussed previously (Suzuki et al., 1996) . From comparison with the radioactivity of acetylserine, it was calculated that~3% of the tRNA Ser CAG was attached with acetylleucine. These results were reproducible.