Transcription factor acting negatively in the phytochrome B signaling pathway under prolonged red light. Regulates PHYB abundance at the post-transcriptional level, possibly via the ubiquitin-proteasome pathway. May regulate the expression of a subset of genes by binding to the G-box motif. Homodimer (Probable). Interacts specifically with the Pfr form of phytochrome B. Migrates rapidly to speckles upon light exposure. Expressed in flowers. Barely detectable in dark-grown seedlings. Induced after 2 hours of light exposure. By red light. Stable upon light exposure. The active phytochrome binding (APB) motif (3-17) is involved in interaction with PHYB. The Gln-rich domain in the C-terminal region functions to modulate the transcriptional activity of BHLH72/PIF7. Not phosphorylated upon light exposure. Plants are hypersensitive to red light, exhibiting shorter hypocotyls and larger cotyledons.