MOLECULAR MECHANISMS OF VARIATION AND ADAPTATION IN BORRELIA BURGDORFERI

我们的总体目标是了解疏螺旋体 伯氏杆菌建立了一种感染：扁虱之间的传播循环 媒介和哺乳动物的宿主，这两者都是维持 自然界中的螺旋体。以下是与此相关的研究工作 进球。 1.外表面蛋白变异。B.外膜； 伯氏杆菌含有几种大小不等的丰富蛋白质(Osp)。 和表达式，并具有未知功能。很可能是因为 不同的OSP赋予螺旋体不同的属性，这些属性 与它必须生存的不同环境相关。Dr。 马戈利斯克隆并测序了一个OspC基因，该基因在 大可变膜蛋白的培养及其同源成员 在B.Hermsii的家人。对已鉴定的启动子区域进行分析 RNA或DNA中可能影响基因的潜在二级结构 表情。SpC上游是与2-嘌呤同源的序列 生物合成酶；这些gua基因的质粒位置是唯一的 可能反映了对不同的嘌呤水平的适应 扁虱对抗哺乳动物。蒂利博士已经证明了这些基因中的一个 通过补充缺失的大肠杆菌突变体来编码功能产物 在这种酶中。重叠的不同启动子可能允许联合 OspC和GUA基因的调控表达。 2.质粒结构与复制。了解其结构和 不同寻常的线形和环状螺旋体基因组的复制是 与生俱来的兴趣和实际价值。蒂利医生已经对疏螺旋体进行了检测 与端粒序列结合的蛋白质的提取物。她已经孤立了 并对胡疏螺旋体的同源基因进行了测序，该基因可能是 参与线形质粒结构和复制。她已经决定 该区域的遗传组织，其中包括两个未知的开放 Rho和rpsT基因的阅读框架和同源物及其互补 在一些同源基因上有缺陷的大肠杆菌突变体。霍根和罗莎 使用由Fuhrman建造的图书馆从OspAB逆流而上 操纵子朝向49kb线性质粒的端粒，这是 预测与先前克隆的序列不同的序列。霍根 已经确定了一种不寻常的序列整合事件的证据 从一个循环质粒到另一个循环质粒。

Our broad objective is to understand the means by which Borrelia burgdorferi establishes an infection:transmission cycle between the tick vector and mammalian reservoir host, both of which are needed to maintain the spirochete in nature. The following research efforts relate to this goal. 1. Outer surface protein variation. The outer membrane of B. burgdorferi contains several abundant proteins (Osps) that vary in size and expression and are of unknown function. It is likely that the different Osps confer distinct properties on the spirochete that are pertinent to the different environments in which it must survive. Dr. Margolis cloned and sequenced an ospC gene that is variably expressed in culture and homologous to members of the large variable membrane protein family in B. hermsii. Analysis of the promoter region identified potential secondary structure in the RNA or DNA that could influence gene expression. Upstream of ospC are sequences homologous to 2 purine biosynthesis enzymes; the plasmid location of these gua genes is unique to Borrelia and may reflect an adaptation to disparate purine levels in ticks versus mammals. Dr. Tilly has demonstrated that one of these genes encodes a functional product by complementing an E. coli mutant deficient in this enzyme. Overlapping divergent promoters could permit co- regulated expression of the ospC and gua genes. 2. Plasmid structure and replication. Understanding the structure and replication of the unusual linear and circular Borrelia genome is of intrinsic interest and practical merit. Dr. Tilly has assayed Borrelia extracts for proteins that bind to telomeric sequences. She has isolated and sequenced the gene for the Borrelia HU homolog, a gene that may be involved in linear plasmid structure and replication. She has determined the genetic organization of the region, which includes two unknown open reading frames and homologs of the rho and rpsT genes and complemented E. coli mutants defective in some homologous genes. Hogan and Rosa have used a library constructed by Fuhrman to walk upstream from the ospAB operon toward the telomere of the 49-kb linear plasmid, which is predicted to have different sequence from those previously cloned. Hogan has identified evidence for an unusual integration event of sequences from one circular plasmid into another.