ASK1, Active (ZTL) Active Protein

Function: 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. Ref.1 Ref.2 Ref.3 Ref.4 Ref.12 Ref.13 Ref.14 Ref.15 Ref.16

Pathway: Protein modification; protein ubiquitination.

Subunit structure: 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. Ref.4 Ref.9 Ref.11 Ref.13 Ref.14 Ref.15 Ref.16 Ref.17

Subcellular location: Nucleus. Cytoplasm. Note: 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). Ref.3 Ref.15 Ref.16

Tissue specificity: Ubiquitously expressed with higher levels in cotyledons and leaves. Ref.2 Ref.3

Developmental stage: Mainly present during the light phase, and degraded in a proteasome-dependent manner in dark (at protein level).

Induction: Not regulated at the transcript level, but circadian-regulation at the protein level with a peak at the end of the subjective day. Ref.1 Ref.3 Ref.10 Ref.15 Ref.17

Post-translational modification: 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

By similarity.

Disruption phenotype: Accumulation of ADO3 protein during the morning period and early flowering time. Ref.16

Miscellaneous: 'Zeitlupe' means slow motion in German.'Adagio' means slowly in Italian.

Sequence similarities: Belongs to the ADAGIO family.Contains 1 F-box domain.Contains 5 Kelch repeats.Contains 1 PAC (PAS-associated C-terminal) domain.Contains 1 PAS (PER-ARNT-SIM) domain.

Sequence caution: The sequence AAK64006.1 differs from that shown. Reason: Frameshift at positions 462 and 467.