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(ADO1) E3 ubiquitin ligase complex is involved in the regulation of circadian clock-dependent processes including the transition to flowering time, hypocotyl elongation, cotyledons and leaf movement rhythms. APRR1/TOC1 and APRR5, but not 'GIGANTEA', are proteolytic substrates of this ubiquitin ligase complex. Blue light enhances cooperative stabilization of 'GIGANTEA' and ADO1/ZTL, leading to amplification and sharpening of the expression profile of APRR1/TOC1. ADO1/ZTL interacts with ADO3, preventing the interaction of ADO3 with CDF1. Protein modification; protein ubiquitination. Interacts with NFXL2. Interacts (via N-terminus) with GI and (via Kelch repeats) with ADO3. Component of an E3 ubiquitin ligase SCF(ADO1) complex composed of SKP1A/ASK1 (or SKP1B/ASK2), CUL1, RBX1 and ADO1. Also interacts with SKP1D/ASK4, SKP1K/ASK11, CRY1, PHYB, APRR1 and APRR5, and probably with SKP1N/ASK14 and SKP1S/ASK19. Nuclear after 9 hours of illumination (afternoon of long days). Cytoplasmic when plant have been subsequently grown 16 hours in light and 5 hours in dark (early morning of long days). A number of isoforms are produced. According to EST sequences. Ubiquitously expressed with higher levels in cotyledons and leaves. Mainly present during the light phase, and degraded in a proteasome-dependent manner in dark (at protein level). Not regulated at the transcript level, but circadian-regulation at the protein level with a peak at the end of the subjective day. May be ubiquitinated. Degraded in a proteasome-dependent manner. FMN binds covalently to cysteine after exposure to blue light and is reversed in the dark. Accumulation of ADO3 protein during the morning period and early flowering time. 'Zeitlupe' means slow motion in German. 'Adagio' means slowly in Italian. Belongs to the ADAGIO family.