ISOLATION AND CHARACTERIZATION OF THE DROSOPHILA RETINAL-DEGENERATION-B (RDGB) GENE

retinal degeneration-B (rdgB) mutants of Drosophila melanogaster undergo rapid light-induced retinal degeneration. We conducted a molecular characterization of the rdgB gene to examine the nature of the gene product. Through the isolation and analysis of X-ray-induced rdgB alleles, the cytogenetic position of the gene was determined to be the 12C1 salivary region. Genomic DNA corresponding to this region was isolated by a chromosomal walk. The chromosomal aberrations associated with the three X-ray-induced rdgB alleles were shown to be within a 5-kb genomic region. A single transcription unit was affected by the alleles, identifying it as the rdgB gene. RNA-RNA Northern hybridization indicated the rdgB gene transcribed five mRNAs ranging in size from 3.9 to 9.5 kb. These mRNAs were expressed in adult heads, but not detected in bodies. Analysis of RNA isolated from wild-type and eyes absent heads indicated that rdgB mRNA expression was not restricted to the retina. DNA sequence analysis of the transcription unit revealed an open reading frame capable of encoding a 116-kD transmembrane protein. The deduced protein shows no overall homology to previously described proteins, but has sequences in common with proposed functional domains of Ca2+-ATPase.