Zhang B, Tao T, Wilson G G, Blumenthal R M
New England BioLabs, Inc., Beverly, MA 01915-5599.
Nucleic Acids Res. 1993 Feb 25;21(4):905-11. doi: 10.1093/nar/21.4.905.
The DNA methyltransferase of the AluI restriction-modification system, from Arthrobacter luteus, converts cytosine to 5-methylcytosine in the sequence AGCT. The gene for this methyltransferase, aluIM, was cloned into Escherichia coli and sequenced. A 525-codon open reading frame was found, consistent with deletion evidence, and the deduced amino acid sequence revealed all ten conserved regions common to 5-methylcytosine methyltransferases. The aluIM sequence predicts a protein of M(r) 59.0k, in agreement with the observed M(r), making M.AluI the largest known methyltransferase from a type II restriction-modification system. M.AluI also contains the largest known variable region of any monospecific DNA methyltransferase, larger than that of most multispecific methyltransferases. In other DNA methyltransferases the variable region has been implicated as the sequence-specific target recognition domain. An in-frame deletion that removes a third of this putative target-recognition region leaves the Alu I methyltransferase still fully active.
来自藤黄节杆菌的AluI限制修饰系统的DNA甲基转移酶，可将序列AGCT中的胞嘧啶转化为5-甲基胞嘧啶。该甲基转移酶的基因aluIM被克隆到大肠杆菌中并进行了测序。发现了一个525个密码子的开放阅读框，与缺失证据一致，推导的氨基酸序列揭示了5-甲基胞嘧啶甲基转移酶共有的所有十个保守区域。aluIM序列预测的蛋白质分子量为59.0k，与观察到的分子量一致，这使得M.AluI成为已知来自II型限制修饰系统的最大甲基转移酶。M.AluI还包含任何单特异性DNA甲基转移酶中已知最大的可变区，比大多数多特异性甲基转移酶的可变区还要大。在其他DNA甲基转移酶中，可变区被认为是序列特异性靶标识别结构域。一个框内缺失去除了这个假定的靶标识别区域的三分之一，但Alu I甲基转移酶仍具有完全活性。
