An Adenosine Deaminase that Generates Inosine at the Wobble Position of tRNAs

Abstract

Several transfer RNAs (tRNAs) contain inosine (I) at the first position of their anticodon (position 34); this modification is thought to enlarge the codon recognition capacity during protein synthesis. The tRNA-specific adenosine deaminase of Saccharomyces cerevisiae that forms I 34 in tRNAs is described. The heterodimeric enzyme consists of two sequence-related subunits (Tad2p/ADAT2 and Tad3p/ADAT3), both of which contain cytidine deaminase (CDA) motifs. Each subunit is encoded by an essential gene ( TAD2 and TAD3 ), indicating that I 34 is an indispensable base modification in elongating tRNAs. These results provide an evolutionary link between the CDA superfamily and RNA-dependent adenosine deaminases (ADARs/ADATs).