Li R, Golden S S
Department of Biology, Texas A&M University, College Station 77843-3258.
Proc Natl Acad Sci U S A. 1993 Dec 15;90(24):11678-82. doi: 10.1073/pnas.90.24.11678.
Three psbA genes encoding the D1 protein of the photosystem II reaction center are differentially expressed under different light intensities in the cyanobacterium Synechococcus sp. strain PCC 7942. Two of the three psbA genes, psbAII and psbAIII, are induced rapidly when light intensity is increased from 125 x 10(-6) mol.m-2.s-1 to 750 x 10(-6) mol.m-2.s-1. A recombinational cloning vector that carries a transcriptional lacZ reporter gene was used to characterize the controlling elements responsible for light induction. At least three distinct cis elements are present in the regulatory regions of pbsAII and psbAIII: basal promoters, comparable to Escherichia coli sigma 70 promoters in position and sequence, confer constitutive expression of the genes under both low and high light intensities; negative elements upstream of the promoters down-regulate the expression of the corresponding gene; and sequences downstream of the promoters that correspond to the untranslated leader regions of the mRNAs (+1 to +41 in psbAII and +1 to +39 in psbAIII) are responsible for increased expression under high light. When these light-responsive elements were combined with an E. coli promoter (conII) in different positions and orientations, the expression of the lacZ gene was induced 4- to 11-fold. The induction of gene expression under high light by these enhancers was position independent but orientation dependent. When the elements were combined with the conII promoter in the correct orientation, they also conferred a small but reproducible level of light-responsive expression on this E. coli promoter.
在集胞藻属蓝细菌PCC 7942中，编码光系统II反应中心D1蛋白的三个psbA基因在不同光照强度下差异表达。当光照强度从125×10⁻⁶ mol·m⁻²·s⁻¹增加到750×10⁻⁶ mol·m⁻²·s⁻¹时，三个psbA基因中的两个，即psbAII和psbAIII，会迅速被诱导表达。一个携带转录型lacZ报告基因的重组克隆载体被用于鉴定负责光诱导的调控元件。在pbsAII和psbAIII的调控区域中至少存在三种不同的顺式元件：基础启动子，其位置和序列与大肠杆菌σ⁷⁰启动子相似，在低光照和高光照强度下均赋予基因组成型表达；启动子上游的负调控元件下调相应基因的表达；启动子下游与mRNA的非翻译前导区相对应的序列（psbAII中为+1至+41，psbAIII中为+1至+39）负责高光照下表达的增加。当这些光响应元件与大肠杆菌启动子（conII）以不同的位置和方向组合时，lacZ基因的表达被诱导4至11倍。这些增强子在高光照下对基因表达的诱导与位置无关，但与方向有关。当元件以正确的方向与conII启动子组合时，它们也赋予了这个大肠杆菌启动子一个小但可重复的光响应表达水平。
