Restrepo B I, Carter C J, Barbour A G
Department of Microbiology, University of Texas Health Science Center, San Antonio 78284-7758.
Mol Microbiol. 1994 Jul;13(2):287-99. doi: 10.1111/j.1365-2958.1994.tb00423.x.
The relapsing fever agent, Borrelia hermsii, undergoes multiphasic antigenic variation to evade its host's immune response. A frequently observed switch is serotype 7 to 26. Unlike silent vmp genes previously characterized, the transcriptionally silent vmp26 sequence was a pseudogene in lacking a start codon. In serotype 7 the location of the silent vmp26 sequence just downstream of vmp7 on the expression plasmid, as well as on the silent plasmid, was also unique. The demonstration of a predicted circular recombination product in serotype 7 but not serotype 21 populations indicates that the pseudogene was activated by an intramolecular recombination producing a deletion of DNA between 20-nucleotide direct repeats in vmp7 and psi vmp26.
复发性发热病原体赫氏疏螺旋体（Borrelia hermsii）会经历多阶段抗原变异以逃避宿主的免疫反应。一种常见的转变是血清型7到26。与先前鉴定的沉默vmp基因不同，转录沉默的vmp26序列是一个假基因，缺乏起始密码子。在血清型7中，沉默的vmp26序列在表达质粒以及沉默质粒上位于vmp7下游的位置也很独特。在血清型7群体中而非血清型21群体中检测到预测的环状重组产物，这表明该假基因通过分子内重组被激活，导致vmp7和假vmp26中20个核苷酸直接重复序列之间的DNA缺失。
