Tad2 is part of the functional heterodimeric deaminase Tad2/3. At variance with other dimeric ADAT2/3 deaminases, T. brucei Tad2/3 contains only one functional zinc ion, out of the two per dimeric enzyme. The C-terminal end of subunit tbTad2 plays a critical role in tRNA binding, while subunit Tad3 contributes to catalysis - it is not simply a structural component. This tRNA A:I editing enzyme plays a role in both A:I editing in position 34 and C:U editing in position 32 in vivo. In vitro, this A-to-I tRNA deaminase catalyzes also C-to-U deamination of DNA. The A34-to-I34 deamination reaction was tested with T. brucei tRNA-Thr as substrate. However, as other eukaryotic heterodimeric Tad2/3 it also works on other naturally occurring A34-containing tRNA (Alfonzo J. , unpublished data).