Direct Targeting of Light Signals to a Promoter Element-Bound Transcription Factor
Jaime F. Martínez-García,
Enamul Huq,
Peter H. Quail
*
Light signals perceived by the phytochrome family of
sensory photoreceptors are transduced to photoresponsive genes by an unknown mechanism. Here, we show that the basic helix-loop-helix transcription factor PIF3 binds specifically to a G-box DNA-sequence motif present in various light-regulated gene promoters, and that phytochrome B binds reversibly to G-box-bound PIF3 specifically upon
light-triggered conversion of the photoreceptor to its biologically active conformer. We suggest that the phytochromes may function as
integral light-switchable components of transcriptional regulator complexes, permitting continuous and immediate sensing of changes in
this environmental signal directly at target gene promoters.
Department of Plant and Microbial Biology, University of
California, Berkeley, CA 94720, and U.S. Department of
Agriculture-Agricultural Research Service Plant Gene Expression
Center, 800 Buchanan Street, Albany, CA 94710, USA.
*
To whom correspondence should be addressed. E-mail:
quail{at}nature.berkeley.edu
