Pre-mRNA editing involving the conversion of adenosine to inosine is mediated by 
adenosine deaminases that act on RNA (ADAR1 and ADAR2). ADARs contain multiple 
double-stranded RNA(dsRNA)-binding domains in addition to an adenosine deaminase 
domain. An adenosine deaminase acting on tRNAs, scTad1p (also known as scADAT1), 
cloned from Saccharomyces cerevisiae has a deaminase domain related to the ADARs 
but lacks dsRNA-binding domains. We have identified a gene homologous to scADAT1 
in the region of Drosophila melanogaster Adh chromosome II. Recombinant 
Drosophila ADAT1 (dADAT1) has been expressed in the yeast Pichia pastoris and 
purified. The enzyme has no activity on dsRNA substrates but is a tRNA deaminase 
with specificity for adenosine 37 of insect alanine tRNA. dADAT1 shows greater 
similarity to vertebrate ADARs than to yeast Tad1p, supporting the hypothesis of 
a common evolutionary origin for ADARs and ADATs. dAdat1 transcripts are 
maternally supplied in the egg. Zygotic expression is widespread initially and 
later concentrates in the central nervous system.