Enables myosin binding activity. Involved in several processes, including determination of adult lifespan; mating behavior; and system process. Located in endoplasmic reticulum and membrane. Expressed in several structures, including egg-laying apparatus; ganglia; gonad; non-striated muscle; and tail hypodermis. Human ortholog(s) of this gene implicated in several diseases, including Alzheimer's disease; Gillespie syndrome; autosomal dominant cerebellar ataxia (multiple); and diabetes mellitus (multiple). Is an ortholog of human ITPR1 (inositol 1,4,5-trisphosphate receptor type 1); ITPR2 (inositol 1,4,5-trisphosphate receptor type 2); and ITPR3 (inositol 1,4,5-trisphosphate receptor type 3).