MOLECULAR AND IMMUNOLOGICAL CHARACTERIZATION OF A GQ PROTEIN FROM VENTRAL AND LATERAL EYE OF THE HORSESHOE-CRAB LIMULUS-POLYPHEMUS

GTP binding proteins of the Gq family have been implicated in phototra nsduction in rhabdomeral photoreceptors. In this study we used molecul ar and immunochemical techniques to characterize a GTP-binding protein a subunit of the Gq family in ventral and lateral photoreceptors of t he horseshoe crab, Limulus polyphemus. Both ventral photoreceptors and lateral eye retinular cells became strongly labeled with an antibody directed against che common carboxyl tail of two Gq family proteins, G alpha(q) and G alpha(11). This antibody also labeled a 42 kDa band on Western blots of proteins from ventral photoreceptor cell bodies, ven tral photoreceptor axons, lateral eyes and lateral optic nerves. The r everse transcription-polymerase chain reaction (RT-PCR), along with de generate oligonucleotide primers designed against conserved regions of known G alpha q and G alpha(11) proteins, was used to isolate a cDNA from ventral eye RNA which encodes a protein with high identity to kno wn Gq proteins. Ribonuclease protection assays showed chat the corresp onding message was expressed in ventral eye, but these assays, as well as Northern blots, failed to detect expression in lateral eye. Theref ore, while photoreceptors of both ventral and lateral eyes contain a G q-like protein, che mRNA encoding the Gq protein in the ventral eye ma y differ in nucleotide sequence from its lateral eye counterpart.