10         20         30         40         50         60
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MQEQATSSLA ASSLPSSSER SSSSAPHLEI KEGIESDEEI RRVPEFGGEA VGKETSGRES - 60
GSATGQERTQ ATVGESQRKR GRTPAEKENK RLKRLLRNRV SAQQARERKK AYLSELENRV - 120
KDLENKNSEL EERLSTLQNE NQMLRHILKN TTGNKRGGGG GSNADASL

HY5 gene encodes a basic leucine zipper (bZIP) transcription factor that positively regulates photomorphogenesis. The HY5 protein is constitutively localized in the nucleus and is involved in light-dependent regulation of transcription from promoters that contain a G-box, one of several light-response elements. Acts downstream of the light receptor network and directly affects transcription of light-induced genes. Specifically involved in blue-light specific pathway, suggesting that it participates in transmission of cryptochromes (CRY1 and CRY2) signals to downstream responses. In darkness, its degradation prevent the activation of light-induced genes. Physical and genetic interactions between HY5 and COP1 (a repressor of photomorphogenetic development) negatively regulate the level and activity of HY5 in a light-dependent manner. In darkness, COP1 is enriched in the nucleus and interacts with HY5, resulting in 26S proteasome-mediated degradation of HY5. By contrast, in the light, COP1 is localized in the cytoplasm, and HY5 is stable and exists in abundance in the nucleus. Thus, light ultimately regulates the abundance of HY5 by regulating nuclear COP1 levels. Transcription factor that promotes photomorphogenesis in the light. Acts downstream of the light receptor network and directly affects transcription of light-induced genes. Specifically involved in blue-light specific pathway, suggesting that it participates in transmission of cryptochromes (CRY1 and CRY2) signals to downstream responses. In darkness, its degradation prevent the activation of light-induced genes.