BACKGROUND: ADARs are RNA editing enzymes that target double stranded RNA and 
convert adenosine to inosine, which is read by translation machinery as if it 
were guanosine. Aside from their role in generating protein diversity in the 
central nervous system, ADARs have been implicated in the hypermutation of some 
RNA viruses, although why this hypermutation occurs is not well understood.
RESULTS: Here we describe the hypermutation of adenosines to guanosines in the 
genome of the sigma virus--a negative sense RNA virus that infects Drosophila 
melanogaster. The clustering of these mutations and the context in which they 
occur indicates that they have been caused by ADARs. However, ADAR-editing of 
viral RNA is either rare or edited viral RNA are rapidly degraded, as we only 
detected evidence for editing in two of the 104 viral isolates we studied.
CONCLUSION: This is the first evidence for ADARs targeting viruses outside of 
mammals, and it raises the possibility that ADARs could play a role in the 
antiviral defences of insects.