Figure 1.

Primary structures of ADARs and ADATs (adenosine deaminases acting on tRNAs), showing arrangements of dsRNA-binding domains and deaminase domains. The deaminase motifs (I-III) consist of four or five highly conserved amino acids surrounding each of the cytosines and histidines that bind zinc. Proteins have been drawn to scale and are aligned at the catalytic glutamate residue (E) in the active site in adenosine deaminase motif I. The deaminase domains of ADAR and ADAT1 proteins are larger than the core deaminase domain (which we define as the region of homology between Tad2/ADAT2 and Tad3/ADAT3) because of the insertion of sequence between the second and third zinc-chelating residues, separating deaminase motifs II and III, and probably also because of fusion with a carboxy-terminal subdomain of unknown origin. Abbreviation: aa, amino acids.