Genome analysis of the fruit fly Drosophila melanogaster reveals three new 
ligand-gated ion channel subunits with the characteristic YXCC motif found only 
in alpha-type nicotinic acetylcholine receptor subunits. The subunits are 
designated Dalpha5, Dalpha6, and Dalpha7. Cloning of the Dalpha5 embryonic cDNAs 
reveals an atypically large N terminus, part of which is without identifiable 
sequence motifs and is specified by two polymorphic alleles. Embryonic clones 
from Dalpha6 contain multiple variant transcripts arising from alternative 
splicing as well as A-to-I pre-mRNA editing. Alternative splicing in Dalpha6 
involves exons encoding nAChR functional domains. The Dalpha6 transcript is a 
target of the Drosophila adenosine deaminase acting on RNA (dADAR). This is the 
first case for any organism where a nAChR gene is the target of mRNA editing. 
Seven adenosines could be modified in the extracellular ligand-binding region of 
Dalpha6, four of which are also edited in the Dalpha6 ortholog in the tobacco 
budworm Heliothis virescens. The conservation of an editing site between the 
insect orders Diptera and Lepidoptera makes nAChR editing the most 
evolutionarily conserved invertebrate RNA editing site so far described. These 
findings add to our understanding of nAChR subunit diversity, which is increased 
and regulated by mechanisms acting at the genomic and mRNA levels.