Trautner T A, Pawlek B, Behrens B, Willert J
Max-Planck-Institut für molekulare Genetik, Berlin, Germany.
EMBO J. 1996 Mar 15;15(6):1434-42.
A large portion of the sequences of type II DNA-(cytosine-C5)-methyltransferases (C5-MTases) represent highly conserved blocks of amino acids. General steps in the methylation reaction performed by C5-MTases have been found to be mediated by some of these domains. C5-MTases carry, in addition at the same relative location, a region variable in size and amino acid composition, part of which is associated with the capacity of each C5-MTase to recognize its characteristic target. Individual target-recognizing domains (TRDs) for the targets CCGG (M), CC(A/T)GG (E), GGCC (H), GCNGC (F) and G(G/A/T)GC(C/A/T)C (B) could be identified in the C-terminal part of the variable region of multispecific C5-MTases. With experiments reported here, we have established the organization of the variable regions of the multispecific MTases M.SPRI, M.phi3TI, M.H2I and M.rho 11SI at the resolution of individual amino acids. These regions comprise 204, 175, 268 and 268 amino acids, respectively. All variable regions are bipartite. They contain at their N-terminal side a very similar sequence of 71 amino acids. The integrity of this sequence must be assured to provide enzyme activity. Bracketed by 6-10 'linker' amino acids, they have, depending on the enzyme studied, towards their C-terminal end ensembles of individual TRDs of 38 (M), 39 (E), 40 (H), 44 (F) and 54 (B) amino acids. TRDs of different enzymes with equal specificity have the same size. TRDs do not overlap but are either separated by linker amino acids or abut each other.
II型DNA（胞嘧啶-C5）-甲基转移酶（C5-MTases）的大部分序列代表高度保守的氨基酸块。已发现由C5-MTases执行的甲基化反应的一般步骤由其中一些结构域介导。C5-MTases在相同的相对位置还带有一个大小和氨基酸组成可变的区域，其中一部分与每个C5-MTase识别其特征性靶标的能力有关。在多特异性C5-MTases可变区的C末端部分可以鉴定出针对靶标CCGG（M）、CC（A/T）GG（E）、GGCC（H）、GCNGC（F）和G（G/A/T）GC（C/A/T）C（B）的各个靶标识别结构域（TRDs）。通过本文报道的实验，我们已经在单个氨基酸的分辨率上确定了多特异性MTases M.SPRI、M.phi3TI、M.H2I和M.rho 11SI可变区的结构。这些区域分别包含204、175、268和268个氨基酸。所有可变区都是二分的。它们在N末端一侧包含一个非常相似的71个氨基酸的序列。必须确保该序列的完整性以提供酶活性。由6-10个“连接子”氨基酸括起来，根据所研究的酶的不同，它们在C末端有38（M）、39（E）、40（H）、44（F）和54（B）个氨基酸的单个TRDs集合。具有相同特异性的不同酶的TRDs大小相同。TRDs不重叠，而是由连接子氨基酸隔开或彼此邻接。
