Plays a role in the regulation of circadian rhythms (PubMed:17555964, PubMed:17578907, PubMed:17578908, PubMed:27814361). Transcriptional repressor which inhibits Clock-mediated transcriptional activation by binding to E boxes in the promoters of Clock target genes and repressing their transcription (PubMed:17555964, PubMed:17578907, PubMed:17578908, PubMed:27814361). E box binding activity is time-dependent with higher binding activity seen in the early morning (zeitgeber time 2) than early evening (zeitgeber time 14) and is dependent on the presence of the circadian protein per (PubMed:27814361). It is likely that per binds to Clock-cycle heterodimers, reducing their affinity for E box binding and allowing cwo to bind instead (PubMed:27814361). Negatively regulates its own expression (PubMed:17578908, PubMed:18375860). Expressed in adult brain where it is detected in the dorsal lateral neurons, small and large ventral lateral neurons and dorsal neurons 1, 2 and 3 (at protein level) (PubMed:17578908). Expressed at constant levels in a 12 hour light/12 hour day cycle (at protein level) (PubMed:27814361). Strongly expressed in pacemaker neurons (PubMed:17578907). In adults, mRNA expression oscillates in a circadian manner with a peak at around 14 h Zeitgeber time (PubMed:17578907). mRNA levels oscillate in a rhythmic manner in both 12 hour light/12 hour dark and constant dark conditions with a morning peak around the time of lights-on and an evening peak around the time of lights-off in light/dark conditions (PubMed:17555964, PubMed:17578908, PubMed:18375860). During stage 8 of embryonic development, expressed in the anterior and posterior midgut primordia and expression in the gut continues throughout embryonic development (PubMed:11102367). During germ band retraction, expression is initiated in many tissues in a prominent segmentally repeated pattern (PubMed:11102367). Later, expression is ubiquitous but has higher levels in segmentally repeated clusters of cells (PubMed:11102367). Expression is also found in cells of the amnioserosa, in the head region, in posterior spiracles and in tracheal trees (PubMed:11102367). Strong circadian locomotor phenotype with most mutants being arrhythmic after 4 days in constant darkness and displaying a long period in both light/dark and constant dark conditions (PubMed:17578907). Delayed evening activity peak in light/dark conditions and robust 26.5 hour rhythms for at least 10 days in constant darkness (PubMed:18375860). Reduced circadian oscillation of Clk target genes per, tim, vri and Pdp1 (PubMed:17578907, PubMed:18375860). RNAi-mediated knockdown results in a lengthened circadian period (PubMed:17555964, PubMed:17578908). The name 'clockwork orange' is based on the Anthony Burgess novel of the same name and derives from the potential clock function and the presence of an Orange domain. Contains a degenerate basic motif not likely to bind DNA. Wrong choice of frame.