Ni M, Tepperman J M, Quail P H
Department of Plant and Microbial Biology, University of California, Berkeley 94720, USA.
Nature. 1999 Aug 19;400(6746):781-4. doi: 10.1038/23500.
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.
光敏色素光受体家族通过响应红光和远红光光子的顺序吸收，在生物活性和活性构象之间切换来指导植物基因表达。已经鉴定出几种在光敏色素信号通路后期起作用的中间体，但在该通路早期起作用的中间体较少。我们克隆了一种核碱性螺旋-环-螺旋蛋白PIF3，它可以与光敏色素A和B的非光活性羧基末端片段结合，并在体内的光敏色素信号传导中发挥作用。在这里，我们表明全长光活性光敏色素B仅在光诱导转化为其活性形式后才在体外与PIF3结合，而光转化回其非活性形式会导致与PIF3解离。我们得出结论，光敏色素B的光感信号传导涉及光诱导的、对假定转录调节因子PIF3的构象特异性识别，为基因表达的直接光调节提供了一种潜在机制。
