Titheradge A J, King J, Ryu J, Murray N E
Institute of Cell and Molecular Biology, University of Edinburgh, King's Buildings, Edinburgh EH9 3JR, UK.
Nucleic Acids Res. 2001 Oct 15;29(20):4195-205. doi: 10.1093/nar/29.20.4195.
Current genetic and molecular evidence places all the known type I restriction and modification systems of Escherichia coli and Salmonella enterica into one of four discrete families: type IA, IB, IC or ID. StySBLI is the founder member of the ID family. Similarities of coding sequences have identified restriction systems in E.coli and Klebsiella pneumoniae as probable members of the type ID family. We present complementation tests that confirm the allocation of EcoR9I and KpnAI to the ID family. An alignment of the amino acid sequences of the HsdS subunits of StySBLI and EcoR9I identify two variable regions, each predicted to be a target recognition domain (TRD). Consistent with two TRDs, StySBLI was shown to recognise a bipartite target sequence, but one in which the adenine residues that are the substrates for methylation are separated by only 6 bp. Implications of family relationships are discussed and evidence is presented that extends the family affiliations identified in enteric bacteria to a wide range of other genera.
目前的遗传学和分子学证据将大肠杆菌和肠炎沙门氏菌中所有已知的I型限制与修饰系统归入四个不同家族之一：IA型、IB型、IC型或ID型。StySBLI是ID家族的创始成员。编码序列的相似性已确定大肠杆菌和肺炎克雷伯菌中的限制系统可能是ID型家族的成员。我们进行了互补试验，证实了EcoR9I和KpnAI属于ID家族。StySBLI和EcoR9I的HsdS亚基氨基酸序列比对确定了两个可变区，每个可变区预计都是一个靶标识别结构域（TRD）。与两个TRD一致，StySBLI被证明能识别一个二分靶标序列，但其中作为甲基化底物的腺嘌呤残基仅相隔6个碱基对。文中讨论了家族关系的影响，并提供了证据，将在肠道细菌中确定的家族归属扩展到广泛的其他属。
