ANTIGENIC VARIATION IN MYCOPLASMAS

支原体在自然界中分布广泛，常见 产生相当大的经济影响的疾病，但几乎没有 关于发病机制的信息是可用的。 而且缺乏有效的控制方法。许多 支原体经历了表面蛋白的快速变化，这些蛋白是 被认为对疾病的发病机制有重要作用。这一问题 这些支原体蛋白的变异是否主要是一种 一种免疫避免机制，或者是一种 创建具有不同功能的细胞(例如，细胞亚群 可能会产生不同的粘连导致组织趋向性)没有 已经解决了。在小鼠病原体肺支原体中， 高频表型变异涉及基因的变化 高度重复的V-1表面抗原影响菌落形态， 有机体对支原体病毒的易感性， 支原体对红细胞的吸附，以及毒力。这个 申请人的实验室最近表明，V-1抗原是 由指定为VSA(可变表面)的基因家族编码 抗原)。VSA表达位点的部分(包括 启动子和编码区的前712个核苷酸)存在 作为染色体上的一个单一拷贝。大多数VSA基因缺乏 表达信号并且是沉默的；只有一个VSA基因在 任何给定的单元格。DNA重排发生在VSA基因座上 结合5‘端高频率改变VSA基因表达 从表达的基因的3‘端结束之前的沉默 吉恩。到目前为止，重排的特征是dna。 发生在特定34个碱基序列中的反转 存在于所有VSA基因中。该序列被称为VRS (VSA重组位点)框中。申请者的长期目标是 以(I)克隆整个VSA基因座并确定其全长 核苷酸序列，从而确定VSA的完整谱系 基因和相关的VRS盒，(Ii)更仔细地检查 DNA重排与VSA基因改变的关系 通过表征高频DNA重排来表达 (Iii)阐明酶的作用机制(S) 通过构建重组负责VSA重排- 缺乏突变体，以及(Iv)探索VSA与 评估基因重排与疾病发病机制 动物模型中的重组酶缺陷突变体。

Mycoplasmas are widely distributed in nature and commonly produce diseases of considerable economic impact, yet little information is available concerning mechanisms of pathogenesis and effective methods of control are unavailable. Many mycoplasmas undergo rapid variations in surface proteins that are thought to be important to disease pathogenesis. The issue of whether variations in these mycoplasmal proteins is primarily a mechanism for immune avoidance or instead a mechanism for creating cells with varied functions (e.g., subpopulations of cells may produce different adhesions leading to tissue tropism) has not been addressed. In the murine pathogen Mycoplasma pulmonis, high-frequency phenotypic variations involving changes in the highly repetitive V-1 surface antigens affect colony morphology, the susceptibility of the organism to mycoplasma viruses, the adsorption of mycoplasmas to red blood cells, and virulence. The applicant's laboratory has recently shown that the V-1 antigens are encoded by a family of genes designated vsa (variable surface antigen). The portion of the vsa expression locus (including the promoter and first 712 nucleotides of the coding region) is present as a single copy in the chromosome. Most vsa genes lack expression signals and are silent; only one vsa gene is expressed in any given cell. DNA rearrangements occur in the vsa locus at a high frequency and alter vsa gene expression by combining the 5' end from the expressed gene with the 3' end of a previously silent gene. The rearrangements characterized thus far are DNA inversions that occur within a specific 34-bp sequence that is present in all vsa genes. This sequence is referred to as the vrs (vsa recombination site) box. The applicant's long-range goals are to (i) clone the entire vsa locus and determine its complete nucleotide sequence, thereby identifying the full repertoire of vsa genes and associated vrs boxes, (ii) examine more closely the association between DNA rearrangements and changes in vsa gene expression by characterizing high-frequency DNA rearrangements that occur within vsa, (iii) elucidate the enxymatic mechanis(s) responsible for vsa rearrangements by constructing recombination- deficient mutants, and (iv) explore the association between vsa gene rearrangements and disease pathogenesis by evaluating recombinase-deficient mutants in animal models.