Mode of replicon fusion mediated by the duplicated insertion sequence IS21 in Escherichia coli.
Mode of replicon fusion mediated by the duplicated insertion sequence IS21 in Escherichia coli.
复制标题
大肠杆菌中重复插入序列 IS21 介导的复制子融合模式。
作者：
C. Reimmann;Dieter Haas
来自广泛宿主范围的IncP质粒R68的插入序列IS21 （2.1 kb）很少转位；相比之下，在衍生物R68.45上发现的IS21串联重复序列在各种革兰氏阴性菌的其他复制子的转位动员中高度活跃。被动员的质粒通过单个IS21拷贝直接连接到R68.45上。在R68.45和pBR325::IS21之间的协整体中观察到IS21串联重复的形成，在RP1::IS21质粒衍生物中，位于两个直接重复的IS21拷贝之间的片段被自发地删除。我们推测，当两个IS21元件的末端在转位或缺失事件中特异性连接时，可以产生IS21串联重复序列。一个由两个直接定向的IS21元件组成的抗性基因不具有转座子的功能。将携带转录和翻译停止信号的omega片段插入IS21串联重复序列的不同位点；通过这种方法可以证明，左侧的IS21元件（在R68.45中靠近卡那霉素抗性基因）在协整形成中的活性是右侧元件的100倍。串联携带IS21和IS21::omega的共轭质粒R751和pBR325衍生物之间的协整在一个复制子连接处包含一个IS21，在另一个复制子连接处包含一个IS21::omega。在IS21重复中，IS21内端被优先识别（可能是由IS21转座酶识别），而外端不需要协整形成。基于这些发现，我们提出了R68.45和其他具有IS21串联重复序列的质粒的保守（简单）转位途径。（摘要删节250字）
The insertion sequence IS21 (2.1 kb) originating from the broad-host-range IncP plasmid R68 transposes infrequently; by contrast, the IS21 tandem repeat found on the derivative R68.45 is highly active in transpositional mobilization of other replicons in a variety of Gram-negative bacteria. The mobilized plasmids are joined to R68.45 by single IS21 copies in direct orientation. The formation of IS21 tandem duplications was observed in cointegrates between R68.45 and pBR325::IS21 and also in an RP1::IS21 plasmid derivative in which a segment located between two directly repeated copies of IS21 was deleted spontaneously. We speculate that IS21 tandem repeats can arise when the termini of two IS21 elements are specifically joined in a transposition or deletion event. A resistance gene flanked by two IS21 elements in direct orientation did not behave as a transposon. The omega fragment carrying transcription and translation stop signals was inserted into various sites of the IS21 tandem repeat; in this way it could be shown that the left IS21 element (which is next to the kanamycin resistance gene in R68.45) was 100 times more active in cointegrate formation than was the right-hand element. Cointegrates between the conjugative plasmid R751 and pBR325 derivatives carrying IS21 and IS21::omega in tandem contained a single IS21 at one replicon junction and a single IS21::omega at the other. In the IS21 duplications the inner IS21 ends were preferentially recognized (presumably by IS21 transposase), whereas the outer termini were not required for cointegrate formation. Based on these findings a conservative (simple) pathway of transposition is proposed for R68.45 and other plasmids with an IS21 tandem repeat.(ABSTRACT TRUNCATED AT 250 WORDS)