近日，上海交通大学邓子新院士团队对DNA骨架硫修饰生物学意义的研究又获得两项突破。聚焦核酸研究的著名国际学术刊物 Nucleic Acids Research 以特写文章（Featured article）发表了由该团队德林副教授主持，博士生徐铁刚和姚芬为共同第一作者的论文——“沙门氏菌中与DNA骨架上硫修饰直接关联的一种新的限制系统”。该论文报道了一种新的宿主专一性限制-修饰系统，它与以前所熟知的DNA甲基化限制-修饰系统截然不同，由7个基因负责，其功能与DNA骨架上的硫修饰直接相关。编辑部在特写中写道：“在沙门氏菌中所发现的这种宿主专一性硫修饰系统看来是细菌为了抵御外源对DNA的限制性所装备的又一种新的细胞防卫机制，它被一种新的途径酶所编码，堪比细菌在依赖于DNA甲基化之外加装了又一套新的防御体系”。
与之相反的另一套全新的细胞防卫系统发现于天蓝色链霉菌中，由贺新义副教授主持，博士生刘光为第一作者，以“一种IV型限制内切酶ScoMcrA对硫修饰和甲基化修饰DNA都切割”为题发表在 PLoS Genetics 上，这种酶不仅可以切割DNA骨架上发生了硫修饰的DNA，还可以切割DNA碱基上发生了甲基化修饰的DNA。另外，这套限制-修饰系统分别位于两个相互排斥的基因组岛上，具有“水火不容”的敌对性，两者同时表达会导致细胞瞬时死亡。论文评审员称这是一篇“重要的、epoch-making”的论文。这项发现是上海交大与中国科学院微生物研究所和英国Leicester大学合作的结晶。
这是邓子新院士团队发现DNA骨架硫修饰以来，瞄准科技界普遍关注的有关DNA硫修饰的生物学，尤其是修饰的生理功能这个重大的科学问题公开发表的新的引人注目的原创性成果，充分显示了我国在此前沿新兴领域持之以恒的开拓性和创新性。与DNA甲基化限制-修饰系统一样，这类新系统的广泛和深度挖掘可能具有重大的分子生物学和生物工程学意义。
目前，DNA骨架硫修饰的研究已成为该团队瞄准前沿，奋力开拓的主要科研方向之一，自他们首次报道DNA硫修饰以来，已先后发表了十余篇相关的系统性研究论文，稳步地把对此新兴领域的研究推向新的高度。
据悉，2010年初，中国微生物学会为了促进、激励和纪念DNA硫修饰这个原创性科学发现，彰显我国基础生命科学领域的显示度和影响力，决定在上海交通大学设立“DNA大分子硫修饰科学发现诞生地”纪念牌。（生物谷Bioon.com）
生物谷推荐原文出处：
Nucl. Acids Res. doi: 10.1093/nar/gkq610
A novel host-specific restriction system associated with DNA backbone S-modification in Salmonella
Tiegang Xu, Fen Yao, Xiufen Zhou, Zixin Deng* and Delin You*
Abstract
A novel, site-specific, DNA backbone S-modification (phosphorothioation) has been discovered, but its in vivo function(s) have remained obscure. Here, we report that the enteropathogenic Salmonella enterica serovar Cerro 87, which possesses S-modified DNA, restricts DNA isolated from Escherichia coli, while protecting its own DNA by site-specific phosphorothioation. A cloned 15-kb gene cluster from S. enterica conferred both host-specific restriction and DNA S-modification on E. coli. Mutational analysis of the gene cluster proved unambiguously that the S-modification prevented host-specific restriction specified by the same gene cluster. Restriction activity required three genes in addition to at least four contiguous genes necessary for DNA S-modification. This functional overlap ensures that restriction of heterologous DNA occurs only when the host DNA is protected by phosphorothioation. Meanwhile, this novel type of host-specific restriction and modification system was identified in many diverse bacteria. As in the case of methylation-specific restriction systems, targeted inactivation of this gene cluster should facilitate genetic manipulation of these bacteria, as we demonstrate in Salmonella.
PLoS Genet. doi:10.1371/journal.pgen.1001253
Cleavage of Phosphorothioated DNA and Methylated DNA by the Type IV Restriction Endonuclease ScoMcrA
Guang Liu1, Hong-Yu Ou1, Tao Wang1, Li Li1, Huarong Tan2, Xiufen Zhou1, Kumar Rajakumar3,4, Zixin Deng1*, Xinyi He1*
1 Laboratory of Microbial Metabolism and School of Life Science and Biotechnology, Shanghai Jiao Tong University, Shanghai, China, 2 State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China, 3 Department of Infection, Immunity, and Inflammation, Leicester Medical School, University of Leicester, Leicester, United Kingdom, 4 Department of Clinical Microbiology, University Hospitals of Leicester National Health Service Trust, Leicester, United Kingdom
Abstract
Many taxonomically diverse prokaryotes enzymatically modify their DNA by replacing a non-bridging oxygen with a sulfur atom at specific sequences. The biological implications of this DNA S-modification (phosphorothioation) were unknown. We observed that simultaneous expression of the dndA-E gene cluster from Streptomyces lividans 66, which is responsible for the DNA S-modification, and the putative Streptomyces coelicolor A(3)2 Type IV methyl-dependent restriction endonuclease ScoA3McrA (Sco4631) leads to cell death in the same host. A His-tagged derivative of ScoA3McrA cleaved S-modified DNA and also Dcm-methylated DNA in vitro near the respective modification sites. Double-strand cleavage occurred 16–28 nucleotides away from the phosphorothioate links. DNase I footprinting demonstrated binding of ScoA3McrA to the Dcm methylation site, but no clear binding could be detected at the S-modified site under cleavage conditions. This is the first report of in vitro endonuclease activity of a McrA homologue and also the first demonstration of an enzyme that specifically cleaves S-modified DNA.
