Schaefer M R, Golden S S
Department of Biochemistry and Biophysics, Texas A&M University, College Station 77843.
J Bacteriol. 1989 Jul;171(7):3973-81. doi: 10.1128/jb.171.7.3973-3981.1989.
The genome of the cyanobacterium Synechococcus sp. strain PCC 7942 contains three psbA genes encoding two forms of the D1 protein: form I, the product of psbAI, differs from form II, the product of both psbAII and psbAIII, at 25 of 360 residues. D1 is essential for photosynthesis as a core component of the photosystem II reaction center. Translational gene fusions between each of the Synechococcus psbA genes and the Escherichia coli lacZ gene were inserted into the chromosome of wild-type Synechococcus sp. at the respective psbA loci to serve as in vivo reporters of psbA expression. beta-Galactosidase activities indicated differential expression of the psbA-lacZ gene fusions related to light availability. Expression of psbAI was 500-fold greater than expression of psbAII and 50-fold greater than psbAIII under similar conditions. As light intensity decreased from 600 microE.m-2.s-1 to 2 microE.m-2.s-1, expression of the psbAI reporter increased eightfold while expression of the psbAII and psbAIII reporters decreased 10-fold, suggesting differential production of the two forms of D1 in photosystem II in response to light availability. Relative levels of psbA-lacZ fusion transcripts directly reflected beta-galactosidase activities in the transformants, although the fusion transcripts were less stable than native psbA messages.
集胞藻属（Synechococcus）sp. 菌株PCC 7942的基因组包含三个编码两种形式D1蛋白的psbA基因：I型，即psbAI的产物，与II型（psbAII和psbAIII的产物）在360个残基中的25个处存在差异。D1作为光系统II反应中心的核心成分，对光合作用至关重要。将集胞藻每个psbA基因与大肠杆菌lacZ基因之间的翻译基因融合体插入野生型集胞藻sp. 的染色体中各自的psbA位点，作为psbA表达的体内报告基因。β-半乳糖苷酶活性表明与光可用性相关的psbA-lacZ基因融合体的差异表达。在相似条件下，psbAI的表达比psbAII高500倍，比psbAIII高50倍。当光强度从600 μE·m-2·s-1降至2 μE·m-2·s-1时，psbAI报告基因的表达增加了8倍，而psbAII和psbAIII报告基因的表达下降了10倍，这表明光系统II中两种形式的D1响应光可用性而产生差异。psbA-lacZ融合转录本的相对水平直接反映了转化体中的β-半乳糖苷酶活性，尽管融合转录本比天然psbA信息更不稳定。
