NOVEL GQ-ALPHA ISOFORM IS A CANDIDATE TRANSDUCER OF RHODOPSIN SIGNALING IN A DROSOPHILA TESTES-AUTONOMOUS PACEMAKER

DGq is the alpha subunit of the heterotrimeric GTPase (G alpha), which couples rhodopsin to phospholipase C in Drosophila vision. We have un covered three duplicated exons in dgq by scanning the GenBank data bas e for unrecognized coding sequences. These alternative exons encode si tes involved in GTPase activity and G beta-binding, NorpA (phospholipa se C)-binding, and rhodopsin-binding, We examined the in vivo splicing of dgq in adult flies and find that, in all but the male gonads, only two isoforms are expressed. One, dgqA, is the original visual isoform and is expressed in eyes, ocelli, brain, and male gonads. The other, dgqB, has the three novel exons and is widely expressed. Remarkably, a ll three nonvisual B exons are highly similar (82% identity at the ami no acid level) to the G(q) alpha family consensus, from Caenorhabditis elegans to human, but all three visual A exons are divergent (61% ide ntity). Intriguingly, we have found a third isoform, dgqC, which is sp ecifically and abundantly expressed in male gonads, and shares the div ergent rhodopsin-binding exon of dgqA. We suggest that DGqC is a candi date for the light-signal transducer of a testes-autonomous photosenso ry clock This proposal is supported by the finding that rhodopsin 2 an d arrestin 1, two photoreceptor-cell-specific genes, are also expresse d in male gonads.