Component of an E3 ubiquitin ligase complex that plays a central role in blue light-dependent circadian cycles. Acts as a blue light photoreceptor, due to the presence of FMN, that mediates light-regulated protein degradation of critical clock components by targeting them to the proteasome complex. The SCF(ADO3) E3 ubiquitin ligase complex is involved in the regulation of circadian clock-dependent processes including transition to flowering time, hypocotyl elongation, cotyledons and leaf movement rhythms. Forms a complex with 'GIGANTEA' (GI) to regulate 'CONSTANS' (CO) expression. Promotes CO expression during the light period of long days by decreasing the stability of CDF1 and CDF2 and by interacting directly with the CO protein and stabilizing it. ADO3 function is mainly GI dependent. Does not act as a regulator of CDF1 transcription. The interactions of ADO1/ZTL and ADO2 with ADO3 prevent its interaction with CDF1. Protein modification; protein ubiquitination. Interacts with ADO1 (via Kelch repeats), ADO2 (via Kelch repeats), SKP1A/ASK1, SKP1B/ASK2, ASK3, SKP1K/ASK11, ASK12, ASK13 and SKP1N/ASK14. Interacts (via Kelch repeats) with CDF1, CDF2 and CDF3. Interacts (via N-terminus) with CO and GI (via N-terminus) in a blue-light-dependent manner. Moves from the nucleus into cytosolic speckles upon interaction with ADO1 and ADO2. Highly expressed in stomata and leaves and to a lower extent in seeds, roots, rosettes, stems and siliques. Also present in sepals and anther filaments. Circadian-regulation. Expression is higher during the late light phase than during the dark phase. FMN binds covalently to cysteine after exposure to blue light and is reversed in the dark. Late flowering. 'Adagio' means slowly in Italian. Belongs to the ADAGIO family.