Component of the circadian clock or downstream effector of clock function (PubMed:2517256, PubMed:31080079). Required for suppressing daytime sleep (siesta) under ambient environmental temperatures. Part of a heat avoidance mechanism that modulates daytime sleep behavior under different environmental temperatures to minimize the risk of heat exposure. Under cooler ambient temperatures, suppresses daytime sleep (siesta) and thus allows for longer periods of daytime activity (PubMed:31080079). Epidermis of newly eclosed adults. Abundantly expressed during pupation and decreases rapidly with age. Expression is under pupal (eclosion) circadian clock control. Expression is under the control of a thermosensitive enhancer element called dmpi8 that is encoded in an intron of the close-by circadian clock gene per. At lower temperatures, splicing efficiency of dmpi8 is increased resulting in an increase in the expression of dyw. RNAi-mediated knockdown in per-expressing cells increases daytime sleep levels whereas night-time sleep levels are relatively unaffected. Named 'daywake' based upon its function in daytime sleep suppression. Belongs to the TO family.