Antibiotic resistance genes are often found in structures bounded by copies of IS26, IS257/IS431 or IS1216 that resemble compound (or composite) transposons. However, because of the mechanisms used by IS26 family members, namely that they form cointegrates but cannot resolve them, none of these structures can move together as a coherent single unit. Apparent transposition of these structures is possible via a 2-step process but only if the IS are in direct orientation. An intermolecular reaction catalysed by the IS-encoded transposase and an intramolecular homologous recombination step can occur in either order. In one route, one of the IS bounding the structure forms a cointegrate between the DNA molecule carrying it and a target molecule. Cointegrates formed by either copy-in or targeted conservative routes contain three directly-oriented IS copies and can be resolved by homologous recombination between specific pairs of IS, with one pair leading to apparent transposition of the whole structure. In the other route, homologous recombination first forms a circular intermediate, a translocatable unit or TU, which is incorporated by the transposase either at a random site or adjacent to another IS copy in a target molecule. We therefore conclude that the transposon-like structures are not compound (or composite) transposons and the nomenclature for them should be revised. We propose that the term “pseudo compound transposon” (PCT), first coined in 1989, should be used to describe those structures where the IS are in direct orientation. Structures with the IS in opposite orientation should not be named as transposons.

通常在由类似于化合物（或复合）转座子的IS 26，IS 257 / IS 431或IS 1216拷贝限制的结构中发现抗生素抗性基因。但是，由于IS 26使用的机制家庭成员，即他们形成协整但无法解决它们，这些结构都无法作为一个连贯的单个单元一起移动。这些结构可以通过两步过程进行明显的转位，但前提是IS处于直接方向。由IS编码的转座酶催化的分子间反应和分子内同源重组步骤可以以任何顺序发生。在一种途径中，结合结构的IS之一在携带它的DNA分子与靶分子之间形成共积分。通过复制或靶向保守途径形成的共整合体包含三个直接定向的IS拷贝，可以通过特定IS对之间的同源重组来解决，其中一对导致整个结构的明显转座。在另一条路线上 同源重组首先形成环状中间体，易位单元或TU，其通过转座酶掺入靶分子中的随机位点或与另一IS拷贝相邻。因此，我们得出的结论是，类似转座子的结构不是复合（或复合）转座子，因此应对其命名进行修改。我们建议，“伪复合转座子”（PCT）一词最早于1989年提出，用于描述IS直接定向的那些结构。IS方向相反的结构不应称为转座子。因此，我们得出的结论是，转座子样结构不是复合（或复合）转座子，因此应对其命名进行修改。我们建议，“伪复合转座子”（PCT）一词最早于1989年提出，用于描述IS直接定向的那些结构。IS方向相反的结构不应称为转座子。因此，我们得出的结论是，类似转座子的结构不是复合（或复合）转座子，因此应对其命名进行修改。我们建议，“伪复合转座子”（PCT）一词最早于1989年提出，用于描述IS直接定位的那些结构。IS方向相反的结构不应称为转座子。