A novel subtype of G-protein-coupled receptor kinase, GRK7, in teleost cone photoreceptors

Two kinds of retinal cDNA fragments (OlGRK-R and -C) encoding the putative G-protein-coupled receptor kinases (GRKs) were isolated from medaka, Oryzias latipes, OlGRK-R appears to be closely related to the rhodopsin kinase (RK) found in the outer segments of mammalian photoreceptors, but the deduced amino acid sequence of OlGRK-C shows less than 50% identity to those of GRKs known to date, suggesting that OlGRK-C is a novel GRK subtype (GRK7). The mRNA of OlGRK-R is detectable in rods, and that of OlGRK-C is found in ail four types of cone photoreceptor. The C-terminal of OlGRK-R has a consensus sequence for farnesylation, whereas, surprisingly, OlGRK-C has a consensus sequence for geranylgeranylation, Our result are consistent with the concept that lower vertebrates have rod-and cone-specific opsin kinases. (C) 1998 Federation of European Biochemical Societies.