MmeI: a minimal Type II restriction-modification system that only modifies one DNA strand for host protection.
MmeI: a minimal Type II restriction-modification system that only modifies one DNA strand for host protection.
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DOI：
10.1093/nar/gkn711
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发表时间：
2008-11
影响因子：
14.9
通讯作者：
Davis, Theodore B.
中科院分区：
文献类型：
--
作者：
Morgan, Richard D.;Bhatia, Tanya K.;Lovasco, Lindsay;Davis, Theodore B.
MmeI是一种不常见的II型限制性内切酶，可用于产生长序列标签。我们克隆了MmeI限制修饰（R-M）系统，发现它由一个单一的蛋白质组成，具有内切酶和DNA甲基转移酶活性。该蛋白质包含氨基端核酸内切酶结构域、中心DNA甲基转移酶结构域和C端DNA识别结构域。核酸内切酶在一个位点同时切割两条DNA链，在两个位点结合的酶相互作用以完成切割。在未修饰的DNA上，裂解比甲基转移发生得更快。MmeI仅修饰顶链5′-TCCRAC-3′中的腺嘌呤。MmeI核酸内切酶活性被该顶链腺嘌呤甲基化阻断，并且不受互补链5′-GTYGGA-3′中腺嘌呤甲基化的影响。不存在与MmeI R-M系统相关的额外DNA修饰，如先前表征的IIG型R-M系统所需。因此，MmeI R-M系统仅对两条DNA链中的一条进行修饰以保护宿主。MmeI结构代表了组装限制修饰系统的最小方法，其中单个DNA识别结构域靶向内切核酸酶和DNA甲基转移酶活性。
MmeI is an unusual Type II restriction enzyme that is useful for generating long sequence tags. We have cloned the MmeI restriction-modification (R-M) system and found it to consist of a single protein having both endonuclease and DNA methyltransferase activities. The protein comprises an amino-terminal endonuclease domain, a central DNA methyltransferase domain and C-terminal DNA recognition domain. The endonuclease cuts the two DNA strands at one site simultaneously, with enzyme bound at two sites interacting to accomplish scission. Cleavage occurs more rapidly than methyl transfer on unmodified DNA. MmeI modifies only the adenine in the top strand, 5′-TCCRAC-3′. MmeI endonuclease activity is blocked by this top strand adenine methylation and is unaffected by methylation of the adenine in the complementary strand, 5′-GTYGGA-3′. There is no additional DNA modification associated with the MmeI R-M system, as is required for previously characterized Type IIG R-M systems. The MmeI R-M system thus uses modification on only one of the two DNA strands for host protection. The MmeI architecture represents a minimal approach to assembling a restriction-modification system wherein a single DNA recognition domain targets both the endonuclease and DNA methyltransferase activities.
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