From a group of 436 Drosophila melanogaster cDNA clones, we selected 39 that are expressed exclusively or predominantly in the adult visual system. By sequence analysis, 20 of the clones appear to represent previously unreported distinct cDNAs. The corresponding transcripts are detected in the retina and optic lobes. The genes are scattered throughout the genome, some near mutations known to affect eye function. One of these clones has been identified, by sequence analysis, as the structural gene (Arr) for a Drosophila homolog of human arrestin. Vertebrate arrestin interacts with rhodopsin in phototransduction and has been associated with an autoimmune form of uveitis in primates. The presence of an arrestin homolog in Drosophila suggests that both the vertebrate and invertebrate phototransduction cascades are regulated in a similar manner.

Capacitative Ca ²⁺ entry is a component of the inositol-lipid signaling in which depletion of inositol 1,4,5-trisphosphate (Ins P ₃ )-sensitive Ca ²⁺ stores activates Ca ²⁺ influx by a mechanism that is still unknown. This pathway plays a central role in cellular signaling, which is mediated by many hormones, neurotransmitters, and growth factors. Studies of Drosophila photoreceptors provided the first putative capacitative Ca ²⁺ entry mutant designated transient receptor potential ( trp ) and a Drosophila gene encoding TRP-like protein ( trpl ). It is not clear how the Ca ²⁺ store depletion signal is relayed to the plasma membrane and whether both TRP and TRPL participate in this process. We report here that coexpressing Drosophila TRP and TRPL in Xenopus oocytes synergistically enhances the endogenous Ca ²⁺ -activated Cl ⁻ current and produces a divalent inward current. Both of these currents are activated by Ca ²⁺ store depletion. In the absence of Ca ²⁺ , Mg ²⁺ is the main charge carrier of the divalent current. This current is characterized by lanthanum sensitivity and a voltage-dependent blocking effect of Mg ²⁺ , which is relieved at both hyperpolarizing (inward rectification) and depolarizing (outward rectification) potentials. The store-operated divalent current is neither observed in native oocytes nor in oocytes expressing either TRP or TRPL alone. The production of this current implicates a cooperative action of TRP and TRPL in the depletion-activated current.