The long-term objective of this proposal is to elucidate the biochemical events modulated by CaBPs, the members of a novel subfamily of Ca2+-binding proteins that I have recently identified, in the retina. Ca2+ ions play a critical role in the visual process. While Ca2+ ions modulate some activities directly, they more often exert their effect via Ca2+-binding proteins. This study will investigate the function of CaBP4, a novel photoreceptor-specific Ca2+-binding protein. The localization of CaBP4 at the ciliary axoneme suggests that CaBP4 is involved in the trafficking of signal transduction proteins and/or structural components of outer segments. The importance of photoreceptor trafficking through the cilium has been recognized as mutations in gene products associated with the cilium (myo7A, RP1) have been found in patients with retinal diseases, like Usher syndrome 1B and retinitis pigmentosa. Interference in either the expression or function of Ca2+-binding proteins (GCAPs, recoverin) also leads to ocular pathologies. Therefore, elucidating the function of CaBPs in the retina will not only contribute to our understanding of the basic processes of our vision, but will also allow us to predict which phenotype might result from mutations in their genes and to develop treatments for these diseases. Better understanding the roles of Ca2+-binding proteins may lead to new pharmaceutical therapy strategies for retinal disease, either by directly correcting Ca2+-induced activities caused by a mutated Ca2+-binding protein or by manipulation of the Ca2+ balance within cells to delay cell death. In vitro biochemical procedures and in vivo library screening will be performed to identify putative targets for CaBP4. CaBP4 knockout mice are generated to perform additional in vivo studies and investigate the physiological role of CaBP4. The mechanism of interaction of CaBP4 with its target will also be examined using both in vitro and in vivo procedures.