MECHANISMS OF SULFONAMIDE RESISTANCE IN E. COLI

磺胺类抗生素阻止还原产物的生物合成 抑制腐植酸生成的叶酸化合物 从6-羟甲基蝶呤焦磷酸和p- 氨基苯甲酸酯(PABA)。一种常见的抵抗模式 大肠杆菌中的磺胺类抗生素是通过突变 编码H_2翼酸合成酶的结构基因，从而使 改变的酶产物是一种磺胺抗性形式， 更有效地区分PABA和磺胺类药物 野生型的酶也是如此。磺胺类抗药性 由从中国分离的许多R决定子质粒所赋予 多重耐药的临床大肠杆菌菌株是由 同样的机制：一种磺胺抗性的表达 H_2蝶形酸合成酶。然而，我已经证明了磺胺 大肠埃希菌的耐药性可以通过基因扩增来调节。 虽然我还没有确定被放大的人的身份 基因，编码H_2翼酸合成酶的基因是一个质数 候选，因为该基因产物是磺胺的靶标 抑制力。我是磺胺耐药菌株 特征是有一个8倍的随机扩增的DNA片段 全长18kb。插入序列的关联性(IS5) 与扩增的DNA的一个(或两个)端点一起显示 位点特定(不合法)重组的作用。这项活动是 有别于其他似乎是非法放大的 独立于IS序列。此应用程序建议 确定基因扩增事件的机制，以及 研究H_2蝶形酸合成酶的结构、功能和 在基因水平上的表达。

Sulfonamide antibiotics prevent the biosynthesis of reduced folate compounds by inhibiting the production of H2pteroate from 6-hydroxymethylpterin pyrophosphate and p- aminobenzaoate (PABA). A common mode of resistance to sulfonamide antibiotics in E. coli is via mutation of the structural gene encoding H2pteroate synthase, so that the altered enzyme product is a sulfonamide resistant form that discriminates more effectively between PABA and sulfonamides than does the wild type enzyme. Sulfonamide resistance conferred by many R-determinant plasmids isolated from multiple antibiotic resistant clinical E. coli strains is by the same mechanism: expression of a sulfonamide resistant H2pteroate synthase. However, I have shown that sulfonamide resistance in E. coli can be mediated by gene amplification. Although I have not yet determined the identity of the amplified gene, the gene encoding H2pteroate synthase is a prime candidate, since that gene product is the target of sulfonamide inhibition. The sulfonamide resistant strain that I am characterizing has an 8-fold tandemly amplified DNA segment 18 kb in length. The association of an insertion sequence (IS5) with one (or both) endpoints of the amplified DNA suggests a role for site specific (illegitimate) recombination. This event is distinct from other illegitimate amplifications that seem to be independent of IS sequences. This application proposes to determine the mechanism of the gene amplification event, and to characterize H2pteroate synthase structure, function and expression at the genetic level.