Brown N L, Evans L R
Microbial Molecular Genetics and Cell Biology Group, School of Biological Sciences, University of Birmingham, UK.
Res Microbiol. 1991 Jul-Aug;142(6):689-700. doi: 10.1016/0923-2508(91)90082-l.
Bacteria contain a large number of transposable elements that can be categorized in four major groups according to their mechanisms of transposition. These are: class I: insertion sequences (IS) and compound transposons (with IS sequences at their termini) which usually require only one protein for transposition to occur (e.g. Tn10); class II: complex transposons and insertion sequences with short inverted repeats in which transposition is replicative and requires two gene products (e.g. Tn3); class III: transposable bacteriophage (e.g. Mu). The fourth group consists of the transposons and IS of variable mechanism, which do not fall into the above classes (e.g. Tn7). We have studied the mechanism of transposition of Tn501 and Tn21, closely-related class II mercury-resistance transposons, which transpose via a cointegrate intermediate. By using genetic methods, we have shown that the region of the 989 amino acid transposase between amino acids 57 and 186 determines the specificity for recognition of the 38-bp terminal inverted repeats of the transposon in normal transposition and for replicon fusion catalysed by a single transposon terminus. The Tn501 transposase has been over-expressed and is functional in vivo, raising the frequency of transposition approximately 10(4)-fold.
细菌含有大量可转座元件，根据其转座机制可分为四大类。它们是：第一类：插入序列（IS）和复合转座子（末端带有IS序列），通常转座仅需一种蛋白质（如Tn10）；第二类：复杂转座子和带有短反向重复序列的插入序列，其转座是复制性的，需要两种基因产物（如Tn3）；第三类：可转座噬菌体（如Mu）。第四类由机制可变的转座子和IS组成，不属于上述类别（如Tn7）。我们研究了Tn501和Tn21的转座机制，它们是密切相关的第二类抗汞转座子，通过共整合中间体进行转座。通过遗传学方法，我们表明，在正常转座过程中，989个氨基酸的转座酶中57至186位氨基酸区域决定了对转座子38 bp末端反向重复序列的识别特异性，以及由单个转座子末端催化的复制子融合特异性。Tn501转座酶已被过量表达且在体内具有功能，使转座频率提高了约10⁴倍。
