Hall R M, Collis C M
CSIRO Division of Biomolecular Engineering, Sydney Laboratory, New South Wales, Australia.
Mol Microbiol. 1995 Feb;15(4):593-600. doi: 10.1111/j.1365-2958.1995.tb02368.x.
An integron is a genetic unit that includes the determinants of the components of a site-specific recombination system capable of capturing and mobilizing genes that are contained in mobile elements called gene cassettes. An integron also provides a promoter for expression of the cassette genes, and integrons thus act both as natural cloning systems and as expression vectors. The essential components of an integron are an int gene encoding a site-specific recombinase belonging to the integrase family, an adjacent site, attI, that is recognized by the integrase and is the receptor site for the cassettes, and a promoter suitably oriented for expression of the cassette-encoded genes. The cassettes are mobile elements that include a gene (most commonly an antibiotic-resistance gene) and an integrase-specific recombination site that is a member of a family of sites known as 59-base elements. Cassettes can exist either free in a circularized form or integrated at the attI site, and only when integrated is a cassette formally part of an integron. A single site-specific recombination event involving the integron-associated attI site and a cassette-associated 59-base element leads to insertion of a free circular cassette into a recipient integron. Multiple cassette insertions can occur, and integrons containing several cassettes have been found in the wild. The integrase also catalyses excisive recombination events that can lead to loss of cassettes from an itegron and generate free circular cassettes. Due to their ability to acquire new genes, integrons have a clear role in the evolution of the genomes of the plasmids and transposons that contain them.
整合子是一种遗传单位，它包含位点特异性重组系统各组分的决定因子，该系统能够捕获和移动存在于称为基因盒的移动元件中的基因。整合子还为盒式基因的表达提供启动子，因此整合子既作为天然克隆系统，又作为表达载体发挥作用。整合子的基本组成部分包括：一个int基因，编码属于整合酶家族的位点特异性重组酶；一个相邻位点attI，它被整合酶识别，是基因盒的受体位点；以及一个方向合适的启动子，用于盒式编码基因的表达。基因盒是移动元件，包括一个基因（最常见的是抗生素抗性基因）和一个整合酶特异性重组位点，该位点是被称为59碱基元件的位点家族的成员。基因盒可以以环状游离形式存在，也可以整合在attI位点，只有整合后基因盒才正式成为整合子的一部分。涉及整合子相关的attI位点和盒式相关的59碱基元件的单个位点特异性重组事件会导致游离环状基因盒插入受体整合子。可以发生多个基因盒插入，并且在自然界中已发现含有多个基因盒的整合子。整合酶还催化切除性重组事件，这可能导致基因盒从整合子中丢失并产生游离环状基因盒。由于它们具有获取新基因的能力，整合子在含有它们的质粒和转座子的基因组进化中具有明确的作用。
