Tang Y, Cotterill S, Lichtenstein C P
Department of Biochemistry, Imperial College of Science, Technology and Medicine, London, UK.
Gene. 1995 Aug 30;162(1):41-6. doi: 10.1016/0378-1119(95)92859-6.
Mutations in the terminal 8-bp (5'-T1G2T3G4G5G6C7G8-3') of the inverted repeats of the bacterial transposon, Tn7, were analysed by measuring Tn7 transposition to the attachment site, attTn7. The mutation, C2, present at either end of Tn7 reduces transposition only threefold, but in the double mutant, with C2 at both ends of Tn7, no transposition is detected. C6 mutations have no effect on transposition frequency. Replacement with 5'-A3C4G5C6G7C8-3' at the right end of Tn7 apparently abolishes transposition; yet in the double mutant, where the inverted repeats are restored by substituting this sequence at both ends of Tn7, transposition is partially rescued. This suggests that the mechanism of Tn7 transposition requires communication between the two ends. Tn7 transposition has always been seen to generate a 5-bp target duplication. This is presumed to result from a staggered cut, plus repair synthesis during transposition. We found that two of our right-end mutants, C2 and C6, sometimes yielded a 6-bp target duplication. This observation implies that cleavage of the target site might also involve interaction with the donor ends which, when mutant, relax the specificity for target-site cleavage.
通过测量细菌转座子Tn7向附着位点attTn7的转座情况，对Tn7反向重复序列末端8个碱基对（5'-T1G2T3G4G5G6C7G8-3'）的突变进行了分析。位于Tn7两端的C2突变仅使转座减少三倍，但在Tn7两端均为C2的双突变体中，未检测到转座。C6突变对转座频率没有影响。用5'-A3C4G5C6G7C8-3'替换Tn7右端显然消除了转座；然而，在双突变体中，通过在Tn7两端替换该序列恢复了反向重复序列，转座得到了部分挽救。这表明Tn7转座机制需要两端之间的通信。一直以来，Tn7转座都会产生一个5个碱基对的靶标重复序列。推测这是由交错切割加上转座过程中的修复合成导致的。我们发现，我们的两个右端突变体C2和C6有时会产生一个6个碱基对的靶标重复序列。这一观察结果表明，靶位点的切割可能也涉及与供体末端的相互作用，当供体末端发生突变时，会放宽对靶位点切割的特异性。
