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

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Abstract
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 all 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.