Human, fly, and worm ADAR open reading frames (ORFs) are shown with Z-DNA binding motifs (oval with a Z), dsRBMs (gray ovals), and catalytic domains (blue). Splice forms are designated by a letter of the alphabet following the ADAR name (6), and ORF lengths correlate with the relative number of amino acids for the particular splice-form. Insertions (triangle, apex up) and deletions (triangle, apex down) relative to other splice forms are indicated. An ADAR3 has been detected in mammals, but so far deaminase activity cannot be detected with this protein (26, 27). For comparison an ADAT is also shown.