A substantial fraction of rhodopsin kinase (GRK1) is bound to recoverin (RCVRN) in darkness, when internal Ca2+ levels are high. RCVRN is an EF-hand protein (Murakami et al. 1992) that functions as a myristoyl switch. With Ca2+ bound, the myristoyl group is exposed to attach RCVRN to the membrane. When Ca2+ levels drop with light exposure, Ca2+ dissociates from RCVRN and GRK1 is released. Higher levels of free GRK1 accelerate the phosphorylation and shutoff of photoexcited rhodopsin (MII). However, this feedback mechanism proceeds too slowly to impact the single photon response that was responsible for causing the fall in Ca2+. Instead, it operates during light adaptation, where the light-induced fall in Ca2+ primes the rod to release GRK1 to act after subsequent photoisomerizations of rhodopsin. RCVRN also serves as a Ca2+ buffer within the rod outer segment. Although mutations in RCVRN are not known to cause retinal disease, some cancer-associated retinopathies result from an autoimmune attack on RCVRN (Polans et al. 1991).