title: Binding of phytochrome B to its nuclear signalling partner PIF3 is reversibly induced by light.
abstract: The phytochrome photoreceptor family directs plant gene expression by switching between biologically inactive and active conformers in response to the sequential absorption of red and farred photons. Several intermediates that act late in the phytochrome signalling pathway have been identified, but fewer have been identified that act early in the pathway. We have cloned a nuclear basic helix-loop-helix protein, PIF3, which can bind to non-photoactive carboxy-terminal fragments of phytochromes A and B and functions in phytochrome signalling in vivo. Here we show that full-length photoactive phytochrome B binds PIF3 in vitro only upon light-induced conversion to its active form, and that photoconversion back to its inactive form causes dissociation from PIF3. We conclude that photosensory signalling by phytochrome B involves light-induced, conformer-specific recognition of the putative transcriptional regulator PIF3, providing a potential mechanism for direct photoregulation of gene expression.
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley 94720, USA.
authors.forename: M
authors.initials: M
authors.lastname: Ni
authors.forename: J M
authors.initials: JM
authors.lastname: Tepperman
authors.forename: P H
authors.initials: PH
authors.lastname: Quail
mesh_terms: D017360:Arabidopsis; D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D001665:Binding Sites; D003001:Cloning, Molecular; D004926:Escherichia coli; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D008027:Light; D010786:Photoreceptor Cells; D010834:Phytochrome / Q000235:genetics / Q000378:metabolism*; D051939:Phytochrome B; D011485:Protein Binding / Q000528:radiation effects; D011993:Recombinant Fusion Proteins; D015398:Signal Transduction; D014157:Transcription Factors
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D010834:Phytochrome; D051939:Phytochrome B; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C497952:PHYB protein, Arabidopsis; C116162:PIF3 protein, Arabidopsis