High impact information on HY5

• COP1 interacts directly with HY5 in the nucleus to regulate its activity negatively [1].
• HY5 is a bZIP transcription factor that binds directly to the promoters of light-inducible genes, promoting their expression and photomorphogenic development [1].
• The SUB1 gene encodes a Ca2+-binding protein that suppresses light-dependent accumulation of the transcription factor HY5 [2].
• The COP1-SPA1 interaction defines a critical step in phytochrome A-mediated regulation of HY5 activity [3].
• The accumulation of HYH protein, not the mRNA, is dependent on the presence of HY5 [4].

Biological context of HY5

• Here we show that overexpression of Arabidopsis SPA1 results in a hyperetiolation phenotype and reduced accumulation of HY5 and HFR1 [5].
• Genetic analysis indicates that HYH is predominantly involved in blue-light regulation of development and gene expression, and that the function of HYH in part overlaps with that of HY5 [4].
• In vitro DNA binding studies suggested that HY5 can bind specifically to the G-box DNA sequences but not to any of the other LREs present in the light-responsive promoters examined [6].
• Phosphorylation of HY5 by casein kinase II requires the beta subunit 2, but does not affect HY5's susceptibility to ubiquitination [7].
• Nuclear localization of the HY5 protein strongly suggests that the HY5 gene modulates the signal transduction pathways under the HY5-related development by controlling expression of genes downstream of these pathways [8].

Anatomical context of HY5

• These results, together with previous epistasis studies, support models in which light signals, once perceived by different photoreceptors, converge downstream and act through a common cascade(s) of regulatory steps, as defined by DET1, HY5, COP1, and likely others, to derepress photomorphogenic development [9].

Associations of HY5 with chemical compounds

• HY5 is a point of convergence between cryptochrome and cytokinin signalling pathways in Arabidopsis thaliana [10].
• The Arabidopsis HY5 gene has been defined genetically as a positive regulator of photomorphogenesis and recently has been shown to encode a basic leucine zipper type of transcription factor [6].
• The data also suggest that HY5 and HYH are important negative regulators of auxin signaling amplitude in embryogenesis and seedling development [11].

Physical interactions of HY5

• It was shown that in the dark, COP1 directly interacts with the bZIP transcription factor HY5, a positive regulator of photomorphogenesis, and promotes its proteasome-mediated degradation [4].

Regulatory relationships of HY5

• Here, we show that COP1 negatively regulates HY5, a bZIP protein and a positive regulator of photomorphogenic development [12].
• Moreover, we show that UVR8 regulates expression of the transcription factor HY5 specifically when the plant is exposed to UV-B [13].

Other interactions of HY5

• Furthermore cytokinins are shown to increase levels of HY5 protein accumulation, suggesting that cytokinins may function by reducing HY5 degradation by COP1 (constitutively photomorphogenic 1) [10].
• Among its substrates is the basic domain/leucine zipper (bZIP) transcription factor ELONGATED HYPOCOTYL5 (HY5), one of the key regulators of photomorphogenesis under all light qualities, including UV-B responses required for tolerance to this environmental threat [14].
• Epistatic analyses with the long hypocotyl hy1, hy2, hy3, hy4, and hy5 mutations suggested that these three loci, similar to COP1 and COP9, act downstream of both phytochromes and a blue light receptor, and probably HY5 as well [15].
• Together with our previous studies of CIP7 and HY5, our data suggest that COP1 interacts directly with and regulates multiple physiological targets, which in turn regulate distinct sets of light-regulated responses [16].
• Thus, the COP1-SPA1 interaction defines a critical step in coordinating COP1-mediated ubiquitination and subsequent degradation of HY5 with PHYA signaling [3].

Analytical, diagnostic and therapeutic context of HY5

• Molecular cloning of the HY5 gene using a T-DNA-tagged mutant has revealed that the gene encodes a protein with a bZIP motif, one of the motifs found in transcriptional regulators [8].
• Using limited proteolysis in combination with mass spectrometry, circular dichroism, and nuclear magnetic resonance spectroscopy, we have deduced that the N-terminal 77 amino acids of HY5 form a premolten globular structure, while amino acids 78-110, which constitute the basic region (BR) of the protein, exist in a molten globule state [17].
• Chromatin immunoprecipitation showed that UVR8 associates with chromatin in the HY5 promoter region, providing a mechanistic basis for its involvement in regulating transcription [13].

References