MOLECULAR MECHANISMS OF VARIATION AND ADAPTATION IN BORRELIA BURGDORFERI

我们的总体目标是了解疏螺旋体感染的方式 伯氏螺旋体建立感染：蜱虫之间的传播周期 载体和哺乳动物储库宿主，这两者都需要维持 自然界中的螺旋体以下研究工作与此有关 目标. 1. 外表面蛋白变异。 B的外膜 burgdorferi含有几种丰富的蛋白质（Osps）， 和表达，功能未知。很可能 不同的Osps赋予螺旋体不同的特性， 与它必须生存的不同环境有关。博士 Margolis克隆并测序了一个在大肠杆菌中表达的ospC基因， 与大可变膜蛋白的成员同源 家庭在B。赫姆斯。分析鉴定的启动子区域 RNA或DNA中可能影响基因的潜在二级结构 表情ospC的上游是与2个嘌呤核苷酸同源的序列， 这些gua基因的质粒位置是独特的 并可能反映了不同的嘌呤水平的适应， 蜱虫和哺乳动物蒂利博士证明了这些基因中的一个 通过互补E.大肠杆菌突变缺陷型 在这个酶。 重叠的趋异启动子可以允许共同- 调控ospC和gua基因的表达。 2. 质粒结构和复制。了解结构和 不寻常的线性和环状疏螺旋体基因组的复制是 内在利益和实际价值。蒂利医生化验了包柔螺旋体 提取与端粒序列结合的蛋白质。 她隔离了 并对疏螺旋体HU同源物的基因进行了测序， 参与线性质粒结构和复制。 她决心 该地区的遗传组织，其中包括两个未知的开放 rho和rpsT基因的阅读框和同源物，并互补 E.大肠杆菌中某些同源基因缺陷的突变体。 霍根和罗莎 使用Fuhrman构建的文库从ospAB向上游移动 操纵子朝向49-kb线性质粒的端粒， 预测具有与先前克隆的序列不同的序列。 霍根 已经发现了一个不寻常的序列整合事件的证据 从一个环状质粒转移到另一个

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.