He Xinyi, Ou Hong-Yu, Yu Qing, Zhou Xiufen, Wu Jun, Liang Jingdan, Zhang Wei, Rajakumar Kumar, Deng Zixin
Laboratory of Microbial Metabolism and School of Life Science and Biotechnology, Shanghai Jiaotong University, Shanghai 200030, China.
Mol Microbiol. 2007 Aug;65(4):1034-48. doi: 10.1111/j.1365-2958.2007.05846.x. Epub 2007 Jul 19.
The complete sequence (92 770 bp) of a genomic island (GI) named SLG from Streptomyces lividans 66, encoding a novel DNA S-modification system (dnd), was determined. Its overall G+C content was 67.8%, lower than those of three sequenced Streptomyces genomes. Among 85 predicted open reading frames (ORFs) in SLG, 22 ORFs showed little homology with previously known proteins. SLG displays a mosaic structure composed of four modules, indicative of multiple recombination events in its formation. Spontaneous excision and circularization of SLG was observed, and the excision rate appeared to be induced at least fivefold by MNNG exposure. Using constructed mini-islands of SLG, we demonstrated that Slg01, a P4-like integrase, was sufficient to promote SLG integration, excision and circularization. Eleven counterpart dnd clusters, which also mapped to GIs in 10 chromosomes and a plasmid, were found in taxonomically unrelated bacterial species from various geographic niches. Additionally, c. 10% of actinomycetes were found to possess a dnd cluster in a survey involving 74 strains. Comparison of dnd clusters in the 12 bacteria strongly suggests that these dnd-bearing elements might have evolved from a common ancestor similar to plasmid-originated chromosome II of Pseudoalteromonas haloplanktis TAC125.
测定了来自淡紫灰链霉菌66的一个名为SLG的基因组岛（GI）的完整序列（92770 bp），该序列编码一种新型DNA S-修饰系统（dnd）。其总体G+C含量为67.8%，低于已测序的三个链霉菌基因组。在SLG的85个预测开放阅读框（ORF）中，22个ORF与先前已知的蛋白质几乎没有同源性。SLG呈现出由四个模块组成的镶嵌结构，这表明其在形成过程中发生了多次重组事件。观察到SLG的自发切除和环化，并且MNNG处理似乎至少能将切除率提高五倍。使用构建的SLG迷你岛，我们证明了一种P4样整合酶Slg01足以促进SLG的整合、切除和环化。在来自不同地理生态位的分类学上不相关的细菌物种中，发现了11个对应的dnd簇，它们也定位于10条染色体和一个质粒中的基因组岛。此外，在一项涉及74株菌株的调查中，发现约10%的放线菌拥有一个dnd簇。对这12种细菌中dnd簇的比较强烈表明，这些携带dnd的元件可能起源于一个类似于嗜盐假交替单胞菌TAC125的质粒起源染色体II的共同祖先。
