The development of the Drosophila compound eye requires the function of a set of 
evolutionarily conserved genes. Among these, the Drosophila Pax-6 gene eyeless 
(ey) plays a major role. ey has been considered a master control gene of eye 
development in the animal kingdom because targeted expression of ey and 
vertebrate as well as invertebrate homologs lead to the formation of ectopic 
eyes in Drosophila. We demonstrate that an intron of the ey gene contains an 
enhancer that regulates the eye specific expression of the gene in the eye disc 
primordia of embryos and in the eye imaginal discs of third instar larvae. 
Moreover, a 212-bp enhancer element is necessary and sufficient for the enhancer 
function. It is partially conserved in Drosophila hydei and contains putative 
Pax-6 Paired domain binding sites. We show that several binding sites are 
required for the eye specific expression, and, therefore, we propose a 
Pax-6-like molecule to be a positive transactivator for the eye specific ey 
expression. This transactivator recently has been identified as twin of eyeless, 
the second Pax-6 gene in Drosophila.