Erasmus MC-Sophia Children's Hospital, Laboratory of Pediatrics, Pediatric Infectious Diseases and Immunity, PO Box 2040, 3000 CA Rotterdam, the Netherlands.
Mol Microbiol. 2010 Sep;77(5):1261-77. doi: 10.1111/j.1365-2958.2010.07288.x.
Recombination between repeated DNA elements in the genomes of Mycoplasma species appears to lie at the basis of antigenic variation of several essential surface proteins. It is therefore imperative that the DNA recombinatorial pathways in mycoplasmas be unravelled. Here, we describe the proteins encoded by the Mycoplasma genitalium MG352 and Mycoplasma pneumoniae MPN528a genes (RecU(Mge) and RecU(Mpn) respectively), which share sequence similarity with RecU Holliday junction (HJ) resolvases. RecU(Mge) was found to: (i) bind HJ substrates and large double-stranded DNA molecules and (ii) cleave HJ substrates at the sequence 5'-(G) /(T) C↓(C) /(T) T(A) /(G) G-3' in the presence of Mn(2+). Interestingly, RecU(Mpn) (from M. pneumoniae subtype 2 strains) did not possess obvious DNA binding or cleavage activities, which was found to be caused by the presence of a glutamic acid residue at position 67 of the protein, which is not conserved in RecU(Mge). Additionally, RecU(Mpn) appears not to be expressed by subtype 1 M. pneumoniae strains, as these possess a TAA translation termination codon at position 181-183 of MPN528a. We conclude that RecU(Mge) is a HJ resolvase that may play a central role in recombination in M. genitalium.
在支原体属物种的基因组中，重复 DNA 元件之间的重组似乎是几种重要表面蛋白抗原变异的基础。因此，必须阐明支原体中的 DNA 重组途径。在这里，我们描述了生殖道支原体 MG352 和肺炎支原体 MPN528a 基因（分别为 RecU(Mge)和 RecU(Mpn)）编码的蛋白质，它们与 RecU 霍利迪连接（HJ）解旋酶具有序列相似性。RecU(Mge)被发现：（i）结合 HJ 底物和大双链 DNA 分子，（ii）在 Mn(2+)存在的情况下，在序列 5'-(G)/ (T) C↓(C)/ (T) T(A)/ (G) G-3'处切割 HJ 底物。有趣的是，RecU(Mpn)（来自肺炎支原体亚型 2 株）没有明显的 DNA 结合或切割活性，这是由于该蛋白的第 67 位存在谷氨酸残基所致，而该残基在 RecU(Mge)中不存在保守性。此外，RecU(Mpn)似乎不是由 1 型肺炎支原体菌株表达的，因为这些菌株在 MPN528a 的第 181-183 位具有 TAA 翻译终止密码子。我们得出结论，RecU(Mge)是一种 HJ 解旋酶，可能在生殖道支原体的重组中发挥核心作用。
