Sung S Y, Lavoie C P, Carlyon J A, Marconi R T
Department of Microbiology and Immunology, Medical College of Virginia of Virginia Commonwealth University, Richmond, Virginia 23298-0678, USA.
Infect Immun. 1998 Oct;66(10):4656-68. doi: 10.1128/IAI.66.10.4656-4668.1998.
A series of related genes that are flanked at their 5' ends by a conserved upstream sequence element called the upstream homology box (UHB) have been identified in Borrelia burgdorferi. These genes have been referred to as the UHB or erp gene family. We previously demonstrated that among a limited number of B. burgdorferi isolates, the UHB gene family is variable in composition and organization. Prior to this report the UHB gene family in other species of the B. burgdorferi sensu lato complex had not been studied, and if this family is important in the pathogenesis or biology of the Lyme disease spirochetes, then a wide distribution among species and isolates of the B. burgdorferi sensu lato complex would be expected. To assess this, we screened for the UHB element by Southern hybridization and determined its restriction fragment length polymorphism (RFLP) patterns. The UHB element was found to be carried by all B. burgdorferi sensu lato complex species tested (B. burgdorferi, B. garinii, B. afzelii, B. japonica, B. valaisiana sp. nov., and B. andersonii), but the RFLP patterns varied widely at both the inter- and intraspecies levels. Variation in both the number and size of the hybridizing restriction fragments was evident. PCR analyses also revealed the presence of polymorphic, ospE-related alleles in many isolates. Sequence analyses identified the molecular basis of the polymorphisms as being primarily insertions and deletions. Sequence variation and the insertions and deletions were found to be clustered in two distinct domains (variable domains 1 and 2). In many isolates variable domain 1 is flanked by direct repeat elements, some as long as 38 bp. Computer analyses of the deduced amino acid sequences encoded within variable domain 1 predict them to be hydrophilic, surface exposed, and antigenic. The analyses conducted here suggest that the UHB gene family, as evidenced by the variable UHB RFLP patterns, is not evolutionarily stable and that the polymorphic ospE alleles are derived from a common ancestral gene which has been modified through mutation or recombination events. The characterization of ospE-related genes of the UHB gene family among B. burgdorferi sensu lato species will prove important in attempts to construct a model for UHB gene family organization and in deciphering the role of the UHB gene family in the biology and pathogenesis of the Lyme disease spirochetes.
在伯氏疏螺旋体中，已鉴定出一系列相关基因，这些基因的5'端侧翼是一个称为上游同源框（UHB）的保守上游序列元件。这些基因被称为UHB或erp基因家族。我们先前证明，在数量有限的伯氏疏螺旋体分离株中，UHB基因家族在组成和组织上存在差异。在本报告之前，尚未研究过狭义伯氏疏螺旋体复合群其他物种中的UHB基因家族，并且如果该家族在莱姆病螺旋体的发病机制或生物学中很重要，那么预计它会在狭义伯氏疏螺旋体复合群的物种和分离株中广泛分布。为了评估这一点，我们通过Southern杂交筛选UHB元件，并确定其限制性片段长度多态性（RFLP）模式。发现所有测试的狭义伯氏疏螺旋体复合群物种（伯氏疏螺旋体、伽氏疏螺旋体、阿氏疏螺旋体、日本疏螺旋体、新种瓦莱州疏螺旋体和安德森疏螺旋体）都携带UHB元件，但RFLP模式在种间和种内水平上都有很大差异。杂交限制性片段的数量和大小都存在明显变化。PCR分析还揭示了许多分离株中存在多态性的ospE相关等位基因。序列分析确定多态性的分子基础主要是插入和缺失。发现序列变异以及插入和缺失集中在两个不同的结构域（可变结构域1和2）中。在许多分离株中，可变结构域1侧翼是直接重复元件，有些长达38 bp。对可变结构域1内编码的推导氨基酸序列进行的计算机分析预测它们是亲水性的、表面暴露的且具有抗原性。此处进行的分析表明，如可变的UHB RFLP模式所示，UHB基因家族在进化上不稳定，并且多态性ospE等位基因源自一个通过突变或重组事件而发生改变的共同祖先基因。在狭义伯氏疏螺旋体物种中对UHB基因家族的ospE相关基因进行表征，对于构建UHB基因家族组织模型以及解读UHB基因家族在莱姆病螺旋体生物学和发病机制中的作用将具有重要意义。
