Schnetz K, Rak B
Institut für Biologie III, Universität, Freiburg, Federal Republic of Germany.
Proc Natl Acad Sci U S A. 1992 Feb 15;89(4):1244-8. doi: 10.1073/pnas.89.4.1244.
The cryptic bgl operon of Escherichia coli is activated by the spontaneous insertion of mobile DNA elements. Screening of a collection of such mutations revealed insertion of the 1195-base-pair element IS5 into various positions both upstream and downstream of the bgl promoter P0. Activation of the operon was in all cases attributable to enhancement of P0 activity. Introduction of internal deletions into IS5 almost completely abolished P0 enhancement, demonstrating that enhancement is not simply the result of mutational inactivation of some inhibitory sequences. Intact copies of IS5 in trans restored the enhancing activity of the deletion derivatives. The trans-activator is encoded by IS5 gene ins5A, an essential transposition function. Activation of gene expression by means of interaction of a defective mobile element in cis with functions encoded by a nondefective element in trans has so far been described only for a maize controlling element.
大肠杆菌的隐秘bgl操纵子可被移动DNA元件的自发插入激活。对这类突变体文库的筛选揭示，1195个碱基对的元件IS5插入到了bgl启动子P0上下游的不同位置。在所有情况下，操纵子的激活都归因于P0活性的增强。对IS5进行内部缺失几乎完全消除了P0增强作用，这表明增强作用并非仅仅是某些抑制序列发生突变失活的结果。反式存在的完整IS5拷贝恢复了缺失衍生物的增强活性。反式激活因子由IS5基因ins5A编码，这是一种必需的转座功能。到目前为止，仅在玉米控制元件中描述过通过顺式存在的缺陷型移动元件与反式存在的无缺陷元件所编码的功能相互作用来激活基因表达的情况。
