Wagner D, Quail P H
Department of Plant Biology, University of California, Berkeley 94720, USA.
Proc Natl Acad Sci U S A. 1995 Sep 12;92(19):8596-600. doi: 10.1073/pnas.92.19.8596.
Overexpression of phytochrome B (phyB) in transgenic Arabidopsis results in enhanced deetiolation in red light. To define domains of phyB functionally important for its regulatory activity, we performed chemical mutagenesis of a phyB-overexpressing line and screened for phenotypic revertants in red light. Four phyB-transgene-linked revertants that retain parental levels of full-length, dimeric, and spectrally normal overexpressed phyB were identified among 101 red-light-specific revertants. All carry single amino acid substitutions in the transgene-encoded phyB that reduce activity by 40- to 1000-fold compared to the nonmutagenized parent. The data indicate that the mutant molecules are fully active in photosignal perception but defective in the regulatory activity responsible for signal transfer to downstream components. All four mutations fall within a 62-residue region in the COOH-terminal domain of phyB, with two independent mutations occurring in a single amino acid, Gly-767. Accumulating evidence indicates that the identified region is a critical determinant in the regulatory function of both phyB and phyA.
在转基因拟南芥中过表达光敏色素B（phyB）会导致在红光下黄化现象增强。为了确定phyB对其调节活性起功能作用的结构域，我们对一个phyB过表达株系进行了化学诱变，并在红光下筛选表型回复突变体。在101个红光特异性回复突变体中，鉴定出了4个与phyB转基因连锁的回复突变体，它们保留了亲本水平的全长、二聚体且光谱正常的过表达phyB。所有这些回复突变体在转基因编码的phyB中都携带单个氨基酸替换，与未诱变的亲本相比，其活性降低了40至1000倍。数据表明，突变分子在光信号感知方面完全有活性，但在负责信号向下游组分传递的调节活性方面存在缺陷。所有四个突变都位于phyB羧基末端结构域的一个62个残基的区域内，两个独立的突变发生在单个氨基酸Gly-767上。越来越多的证据表明，所鉴定的区域是phyB和phyA调节功能的关键决定因素。
