PIF3, a phytochrome-interacting factor necessary for normal photoinduced signal transduction, is a novel basic helix-loop-helix protein.
The mechanism by which the phytochrome (phy) photoreceptor family transduces informational light signals to photoresponsive genes is unknown. Using a yeast two-hybrid screen, we have identified a phytochrome-interacting factor, PIF3, a basic helix-loop-helix protein containing a PAS domain. PIF3 binds to wild-type C-terminal domains of both phyA and phyB, but less strongly to signaling-defective, missense mutant-containing domains. Expression of sense or antisense PIF3 sequences in transgenic Arabidopsis perturbs photoresponsiveness in a manner indicating that PIF3 functions in both phyA and phyB signaling pathways in vivo. PIF3 localized to the nucleus in transient transfection experiments, indicating a potential role in controlling gene expression. Together, the data suggest that phytochrome signaling to photoregulated genes includes a direct pathway involving physical interaction between the photoreceptor and a transcriptional regulator.[1]References
- PIF3, a phytochrome-interacting factor necessary for normal photoinduced signal transduction, is a novel basic helix-loop-helix protein. Ni, M., Tepperman, J.M., Quail, P.H. Cell (1998) [Pubmed]
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