Winston J H, Hong L, Datta S K, Kellems R E
Verna and Mars McLean Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030, USA.
Somat Cell Mol Genet. 1996 Jul;22(4):261-78. doi: 10.1007/BF02369566.
Ubiquitously expressed genes contain regulatory features which allow expression in virtually all cell types. In an effort to understand the molecular basis for this regulatory feature, the chromatin structure of the murine adenosine deaminase gene was examined by DNase I digestion in nuclei of several tissues. The promoter contained a strong hypersensitive site in all tissues examined, including those with very high and very low levels of ADA expression. Transgenic mouse studies revealed that a 3.3 kb EcoRI (3.3EE) fragment from intron I was required to generate a strong promoter DNase I hypersensitive site, and to produce ubiquitous expression. The 3.3EE fragment also contained a thymic enhancer activity which mapped to sequences conserved with the human ADA gene T-lymphocyte enhancer. Mutational analysis indicated that ubiquitous expression was not dependent on the presence of a functional thymic enhancer. Both the thymic enhancer and the ubiquitous activator within the 3.3EE fragment functioned with heterologous promoters in transgenic mice.
普遍表达的基因含有调控元件，这些元件使得基因几乎能在所有细胞类型中表达。为了理解这种调控特性的分子基础，通过对几种组织细胞核进行DNase I消化，研究了小鼠腺苷脱氨酶基因的染色质结构。在所检测的所有组织中，包括腺苷脱氨酶（ADA）表达水平非常高和非常低的组织，其启动子都含有一个强烈的超敏位点。转基因小鼠研究表明，来自内含子I的一个3.3 kb EcoRI片段（3.3EE）对于产生一个强烈的启动子DNase I超敏位点以及实现普遍表达是必需的。3.3EE片段还具有胸腺增强子活性，该活性定位于与人ADA基因T淋巴细胞增强子保守的序列上。突变分析表明，普遍表达并不依赖于功能性胸腺增强子的存在。3.3EE片段内的胸腺增强子和普遍激活剂在转基因小鼠中均能与异源启动子发挥作用。
