人型支原体的vaa基因座包含一个编码假定膜蛋白的 divergent 遗传岛。 （注：这里“divergent”不太明确准确的中文意思，可能是“不同的”“分歧的”等，需结合更专业知识确定准确译法）
The vaa locus of Mycoplasma hominis contains a divergent genetic islet encoding a putative membrane protein.
作者信息
Boesen Thomas, Emmersen Jeppe, Baczynska Agata, Birkelund Svend, Christiansen Gunna
机构信息
Department of Medical Microbiology and Immunology, University of Aarhus, DK-8000 Aarhus C, Denmark.
出版信息
BMC Microbiol. 2004 Sep 22;4:37. doi: 10.1186/1471-2180-4-37.
BACKGROUND
The Mycoplasma hominis vaa gene encodes a highly variable, surface antigen involved in the adhesion to host cells. We have analysed the structure of the vaa locus to elucidate the genetic basis for variation of vaa.
RESULTS
Mapping of vaa on existing physical maps of five M. hominis isolates by pulsed field gel electrophoresis revealed that vaa is located in a genomic region containing the majority of other characterized membrane protein genes of M. hominis. Sequencing of an 11 kb region containing the vaa locus of M. hominis isolate 132 showed the presence of conserved housekeeping genes at the borders of the region, uvrA upstream and the hitABL operon downstream to vaa. Analysis of 20 M. hominis isolates revealed that the vaa upstream region was conserved whereas the downstream region was highly variable. In isolate 132 this region contained an open reading frame (ORF) encoding a putative 160 kDa membrane protein. Homologous ORFs were present in half of the isolates, whereas this ORF, termed vmp (variable membrane protein), was deleted from the locus in the remaining isolates. Compellingly, the conserved upstream region and variable downstream region of vaa correlates with the genetic structure of vaa itself which consists of a conserved 5' end and a variable 3' end containing a variable number of exchangeable sequence cassettes.
CONCLUSION
Our data demonstrate that the vaa locus contains a divergent genetic islet, and indicate pronounced intraspecies recombination. The high variability level of the locus indicate that it is a chromosomal 'hot spot', presumably important for sustaining diversity and a high adaptation potential of M. hominis.
背景
人型支原体vaa基因编码一种高度可变的表面抗原，参与对宿主细胞的黏附。我们分析了vaa基因座的结构，以阐明vaa变异的遗传基础。
结果
通过脉冲场凝胶电泳将vaa定位到五株人型支原体分离株的现有物理图谱上，结果显示vaa位于一个基因组区域，该区域包含人型支原体其他大多数已鉴定的膜蛋白基因。对包含人型支原体分离株132的vaa基因座的11 kb区域进行测序，结果显示该区域边界存在保守的管家基因，vaa上游为uvrA，下游为hitABL操纵子。对20株人型支原体分离株的分析表明，vaa上游区域保守，而下游区域高度可变。在分离株132中，该区域包含一个开放阅读框（ORF），编码一种推定的160 kDa膜蛋白。一半的分离株中存在同源ORF，而在其余分离株中，该ORF（称为vmp，可变膜蛋白）从基因座中缺失。引人注目的是，vaa的保守上游区域和可变下游区域与vaa自身的遗传结构相关，vaa自身由保守的5'端和可变的3'端组成，3'端包含可变数量的可交换序列盒。
结论
我们的数据表明vaa基因座包含一个不同的遗传岛，并表明存在明显的种内重组。该基因座的高变异性表明它是一个染色体“热点”，可能对维持人型支原体的多样性和高适应潜力很重要。
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