MOLECULAR-CLONING OF DROSOPHILA RH6 RHODOPSIN - THE VISUAL PIGMENT OFA SUBSET OF R8 PHOTORECEPTOR CELLS

By screening retinal cDNA libraries for photoreceptor-specifically exp ressed genes we have isolated and sequenced a cDNA clone encoding the rhodopsin (Rh6) of a subset of R8 photoreceptor cells of the Drosophil a compound eye. Compared to the other visual pigments of Drosophila, t his rhodopsin is equally homologous to Rh1 and Rh2 (51% amino acid ide ntity) but shows only 32% and 33% amino acid identity with Rh3 and Rh4 , respectively. The open reading frame codes for a protein of 369 amin o acids (MW = 41 691), The primary structure of Rh6 displays sites typ ical for rhodopsin molecules in general, for example, a chromophore bi nding site in transmembrane domain VII, sequence motifs in the intrace llular loops 2 and 3 required for the binding of a heterotrimeric G-pr otein, and a glycosylation site near the N-terminus which seems to be important for protein transport and maturation. Since R8 cells are fou nder cells in the developing compound eye, the isolation of a rhodopsi n gene expressed in these cells may aid the understanding of terminal differentiation of photoreceptor cells. (C) 1997 Federation of Europea n Biochemical Societies.