GENETIC RECOMBINATION IN MYCOPLASMAS

支原体是最小的自由生活微生物，分布广泛。 分布于自然界，通常在植物、昆虫、 还有动物，包括人类。尽管这些措施对经济的影响 疾病是伟大的，但关于机制的信息却很少 目前尚无明确的发病机制和有效的防治方法。这个 支原体的表面特性以大约103的高频变化 每代每个细胞。高频表型变异影响 表面抗原的结构，菌落形态，易感性 有机体对支原体病毒的吸附以及支原体对病毒的吸附 红血球。表面性质的高频变化也 已被证明在疾病的发病机制中起重要作用。一些高频信号 肺支原体的表型变异与 这项提案的重点是特定部位DNA重排。二 同时发生的DNA重排是一个特别有趣的问题 是编码限制性内切酶的新DNA元件的倒置 改装(R-M)系统。另一种涉及编码DNA序列 表位存在于不同的表面抗原中。长期目标是 了解支原体染色体和染色体的分子基础 表型变异，这些现象在疾病中所起的作用 发病机制以及它们在支原体进化中所起的作用。一个 初步假设R-M系统调节染色体DNA 支原体通过双链断裂修复途径的重排。 这种重组机制从根本上不同于已知的 原核生物中重组的途径，这些研究可能已经 对目前关于基因变异的看法产生了相当大的影响 致病细菌这项提案的目标是 鉴定肺支原体的R-M系统，以确定基因的特征 编码可变表面抗原，并确定DNA如何 重排调控这些系统的表达。第一个目标是 在核苷酸水平上克隆和鉴定符合以下条件的遗传位点 与可逆元素高度同源。该基因座可能编码一个 第二个R-M系统。第二个目标是确定DNA倒置是如何 通过检测相关基因的转录调控来影响R-M 精神错乱。第三个目标是灭活肺分枝杆菌的R-M系统 为了确定R-M酶是否在高血压性脑出血中起因果作用。 支原体的频率DNA重排和表型转换。这个 第四个目标是确定DNA重排如何影响 可变表面抗原。这将通过以下方式来实现 编码可变表面抗原的基因和DNA 在他们附近发生的重排。第五个也是最后一个目标是 为了扩大我们包含DNA倒置和其他亚克隆的曲目 重新安排，以便更充分地描述 这一系统中的遗传变异。

Mycoplasmas, the smallest free-living microorganisms, arc widely distributed in nature and commonly produce disease in plants, insects, and animals, including man. Although the economic impact of these diseases is great, little information is available concerning mechanisms of pathogenesis and effective methods of control are unavailable. The surface properties of mycoplasmas vary at a high frequency of about 103 per cell per generation. High-frequency phenotypic variations affect the structure of surface antigens, colony morphology, the susceptibility of the organism to mycoplasma viruses, and the adsorption of mycoplasmas to red blood cells. High-frequency changes in surface properties have also been shown to be important to disease pathogenesis. Some high-frequency phenotypic variations in Mycoplasma pulmonis have been correlated with site-specific DNA rearrangements that are the focus of this proposal. Two DNA rearrangements that occur concurrently are of particular interest One is the inversion of a novel DNA element encoding a restriction and modification (R-M) system. The other involves DNA sequences encoding epitopes present in variable surface antigens. The long-range goals are to understand the molecular basis of mycoplasmal chromosomal and phenotypic variation, the role these phenomena play in disease pathogenesis, and the role they have played in mycoplasmal evolution. A tentative hypothesis is that R-M systems regulate chromosomal DNA rearrangements in mycoplasmas via double-strand break repair pathways. Such a recombination mechanism is fundamentally different from known pathways of recombination in prokaryotes, and these studies may have considerable impact on current thinking regarding genetic variation in pathogenic bacteria The goals of this current proposal are to characterize the R-M systems of M. pulmonis, to characterize the genes encoding the variable surface antigens, and to determine how DNA rearrangements regulate expression of these systems. The first aim is to clone and characterize at the nucleotide level a genetic locus that is highly homologous to the invertible element. This locus may encode a second R-M system. The second aim is to determine how DNA inversion affects R-M by examining the transcriptional regulation of the pertinent loci. The third aim is to inactivate the R-M systems in M. pulmonis in order to determine whether R-M enzymes play a causal role in high- frequency DNA rearrangements and phenotypic switching in mycoplasmas. The fourth aim is to determine how DNA rearrangements affect expression of variable surface antigens. This will be accomplished by characterizing both the genes encoding variable surface antigens and the DNA rearrangements that occur in their vicinity. The fifth and final aim is to expand our repertoire of subclones containing DNA inversions and other rearrangements in order to more fully characterize the potential for genetic variation in this system.