DROSOPHILA RETINAL DEGENERATION A-GENE ENCODES AN EYE-SPECIFIC DIACYLGLYCEROL KINASE WITH CYSTEINE-RICH ZINC-FINGER MOTIFS AND ANKYRIN REPEATS

The Drosophila visual mutant, carrying the retinal degeneration A gene (rdgA), has photoreceptor cells that degenerate within a week after e closion. Morphological studies suggested that this mutant harbors abno rmalities in membrane turnover of the photoreceptor cells. Biochemical ly, the rdgA mutant lacks an eye-specific and membrane-associated diac ylglycerol kinase (DGK; EC 2.7.1.107) activity in a gene-dosage-depend ent manner, suggesting that rdgA gene encodes a DGK. We report the mol ecular cloning and characterization of a DGK gene, which maps to the r dgA locus. This gene, designated as DGK2, has a single open reading fr ame that encodes 1454 amino acids. Like porcine DGK, DGK2 has two cyst eine-rich zinc-finger motifs as well as a DGK catalytic domain. The DG K2 protein contains four ankyrin-like repeats at the C-terminal region , suggesting that DGK2 is likely anchored to the membrane or cytoskele ton. Northern blot analysis and tissue in situ hybridization to adult sections revealed that DGK2 is expressed exclusively in the adult reti na and that the amount of its mRNA is reduced in some of the rdgA muta nt alleles. Furthermore, in two rdgA alleles, rdgA1 and rdgA2, nonsens e and missense mutations occur within their DGK2 gene, respectively. T hus, we conclude that rdgA encodes an eye-specific DGK, the absence of which leads to rhabdomere degeneration due to defective phospholipid turnover.