Deaminates adenosine-34 to inosine in many tRNAs. Heterodimer with tad2. Belongs to the cytidine and deoxycytidylate deaminase family. ADAT3 subfamily. In contrast to other cytidine and deoxycytidylate deaminase, lacks the conserved Glu active site in position 213 which is replaced by a Val residue, suggesting that it acts as a regulatory subunit.