Tran-Betcke A, Behrens B, Noyer-Weidner M, Trautner T A
Gene. 1986;42(1):89-96. doi: 10.1016/0378-1119(86)90153-8.
The phi 3T DNA methyltransferase (Mtase) and most of the SP beta Mtase genes have been sequenced. With the exception of their promoters, no difference was found between the phi 3T and SP beta Mtase genes which code for an enzyme with a Mr of 50 507, consisting of 443 amino acids (aa). Comparison of the deduced aa sequence of the phi 3T/SP beta type Mtase (target specificity: GGCC and GCNGC) with that of the previously established sequence of the SPR Mtase (Buhk et al., 1984) which has the target specificity GGCC and CCGG, reveals strong similarities between these two types of enzymes. There is, however, one striking difference: both the phi 3T/SP beta and the SPR enzymes contain at different positions inserts of 33 aa, which have no homology to each other. We suggest that the methylation specificity unique to each of the two types of Mtases (GCNGC in phi 3T/SP beta; CCGG in SPR) depends on these inserts, while the GGCC-specific modification potential common to all Mtases is determined by structures conserved in both types of enzymes. A DNA fragment of non-modifying phage Z, which shows homology to both flanks of the SPR Mtase gene, was also sequenced. This segment can be described as a derivative of SPR DNA, in which the Mtase gene and sequences at its 5' end have been deleted, with the deletion extending between two direct repeats of 25 bp.
噬菌体φ3T DNA甲基转移酶（Mtase）和大多数SPβ Mtase基因已被测序。除了它们的启动子外，在编码分子量为50 507、由443个氨基酸（aa）组成的一种酶的φ3T和SPβ Mtase基因之间未发现差异。将推导的φ3T/SPβ型Mtase（靶标特异性：GGCC和GCNGC）的氨基酸序列与先前确定的具有靶标特异性GGCC和CCGG的SPR Mtase序列（Buhk等人，1984）进行比较，发现这两种酶之间有很强的相似性。然而，有一个显著的差异：φ3T/SPβ和SPR酶在不同位置都含有33个氨基酸的插入片段，它们彼此没有同源性。我们认为，两种Mtase各自独特的甲基化特异性（φ3T/SPβ中的GCNGC；SPR中的CCGG）取决于这些插入片段，而所有Mtase共有的GGCC特异性修饰潜能则由两种酶中保守的结构决定。未修饰噬菌体Z的一个DNA片段也被测序，该片段与SPR Mtase基因的两侧均显示同源性。这个片段可以描述为SPR DNA的一个衍生物，其中Mtase基因及其5'端的序列已被删除，缺失延伸在两个25 bp的直接重复序列之间。
