The slight reduction in leucylation activity observed in by the results of an additional experiment: incorporation the control variant z-G33G ( Figure 2A ) compared with of [ 14 C]leucine into the tRNA Ser CAG sample with LeuRS native tRNA ( Figure 3A , right-hand graph) was found to was reduced by the addition of SerRS and non-labeled have resulted from the partial deacetylation of 4-acetyl serine to the reaction mixture (data not shown), which cytidine (ac 4 C) due to acid treatment of the 5Ј-half clearly indicates that the same tRNA molecule is comfragment of tRNA Ser CAG (see Materials and methods). petitively aminoacylated by these two enzymes. This is considered further in the Discussion. To conclude that tRNA Ser CAG is aminoacylated with leucine, we carried out a further experiment. The G33 acts as a modulator of leucylation tRNA Ser CAG was charged with serine and serylated In addition to m 1 G37, another unique feature of the serine tRNA Ser CAGs in these Candida species is the presence tRNA Ser CAG was separated from non-aminoacylated The effect of mutation at position 33 in these two each variant was confirmed to have been replaced as expected (shown tRNAs was found to be quite different. In the case of the by arrows).