Ellis J G, Tokuhisa J G, Llewellyn D J, Bouchez D, Singh K, Dennis E S, Peacock W J
CSIRO Division of Plant Industry, Canberra City, A.C.T., Australia.
Plant J. 1993 Sep;4(3):433-43. doi: 10.1046/j.1365-313x.1993.04030433.x.
The structural requirements of the ocs-element, a promoter element in several genes transferred to the host plant nucleus by Agrobacterium tumefaciens and certain DNA viruses, have been further characterized both in vitro and in vivo. Two adjacent and functionally identical protein-binding sites separated by an exact number of nucleotides are required for in vivo activity of the ocs-element. Plant pathogens have presumably recruited cellular transcription factors that interact with these binding sites to drive the high-level expression of their essential genes. Our functional analyses of the ocs-elements from two pathogen promoters define the structure of a sequence motif that might also be expected to occur in plant nuclear genes, and a search of the plant gene database has identified a number of plant gene promoters that contain sequences that resemble the ocs-element. These sequences were analysed for their ability both to bind the maize nuclear protein OCSTF and to activate transcription of an inactive promoter. A functional ocs-element was identified in only one of the plant genes, the soybean heat-shock gene, Gmhsp26-A. The apparent rarity of the ocs-element in plant genes contrasts with its frequent use by pathogens that transform the plant nucleus. Sequences resembling half of an ocs-element, on the other hand, are common in plant promoters and may form part of multi-element control motifs with a variety of regulatory functions. Plant pathogens may, therefore, have evolved to circumvent tight regulatory control of their promoters by the host by duplicating the half ocs-element promoter motifs to take advantage of the ubiquitous ocs-element-binding transcription factors in plants.
章鱼碱合成酶（ocs）元件是根癌土壤杆菌和某些DNA病毒转移至宿主植物细胞核的几个基因中的一种启动子元件，其结构要求已在体外和体内得到进一步表征。ocs元件的体内活性需要两个相邻且功能相同的蛋白质结合位点，二者由精确数量的核苷酸隔开。植物病原体大概招募了与这些结合位点相互作用的细胞转录因子，以驱动其必需基因的高水平表达。我们对来自两种病原体启动子的ocs元件进行的功能分析确定了一种序列基序的结构，这种结构也可能出现在植物核基因中，并且对植物基因数据库的搜索已鉴定出许多含有类似于ocs元件序列的植物基因启动子。分析了这些序列结合玉米核蛋白OCSTF以及激活无活性启动子转录的能力。仅在一种植物基因——大豆热激基因Gmhsp26-A中鉴定出了一个功能性ocs元件。ocs元件在植物基因中明显罕见，这与其在转化植物细胞核的病原体中的频繁使用形成对比。另一方面，类似于半个ocs元件的序列在植物启动子中很常见，并且可能构成具有多种调节功能的多元件控制基序的一部分。因此，植物病原体可能已经进化，通过复制半个ocs元件启动子基序来利用植物中普遍存在的ocs元件结合转录因子，从而规避宿主对其启动子的严格调控。
