Frost L S, Ippen-Ihler K, Skurray R A
Department of Microbiology, University of Alberta, Edmonton, Canada.
Microbiol Rev. 1994 Jun;58(2):162-210. doi: 10.1128/mr.58.2.162-210.1994.
Bacterial conjugation results in the transfer of DNA of either plasmid or chromosomal origin between microorganisms. Transfer begins at a defined point in the DNA sequence, usually called the origin of transfer (oriT). The capacity of conjugative DNA transfer is a property of self-transmissible plasmids and conjugative transposons, which will mobilize other plasmids and DNA sequences that include a compatible oriT locus. This review will concentrate on the genes required for bacterial conjugation that are encoded within the transfer region (or regions) of conjugative plasmids. One of the best-defined conjugation systems is that of the F plasmid, which has been the paradigm for conjugation systems since it was discovered nearly 50 years ago. The F transfer region (over 33 kb) contains about 40 genes, arranged contiguously. These are involved in the synthesis of pili, extracellular filaments which establish contact between donor and recipient cells; mating-pair stabilization; prevention of mating between similar donor cells in a process termed surface exclusions; DNA nicking and transfer during conjugation; and the regulation of expression of these functions. This review is a compendium of the products and other features found in the F transfer region as well as a discussion of their role in conjugation. While the genetics of F transfer have been described extensively, the mechanism of conjugation has proved elusive, in large part because of the low levels of expression of the pilus and the numerous envelope components essential for F plasmid transfer. The advent of molecular genetic techniques has, however, resulted in considerable recent progress. This summary of the known properties of the F transfer region is provided in the hope that it will form a useful basis for future comparison with other conjugation systems.
细菌接合作用导致微生物之间质粒或染色体来源的DNA转移。转移始于DNA序列中一个特定的点，通常称为转移起点（oriT）。接合性DNA转移能力是自我传递性质粒和接合性转座子的特性，它们会动员其他包含相容oriT位点的质粒和DNA序列。本综述将聚焦于接合性质粒转移区域内编码的细菌接合所需基因。最明确的接合系统之一是F质粒的接合系统，自近50年前被发现以来，它一直是接合系统的范例。F转移区域（超过33 kb）包含约40个基因，它们连续排列。这些基因参与菌毛的合成，菌毛是在供体细胞和受体细胞之间建立接触的细胞外细丝；交配对的稳定；在一个称为表面排斥的过程中防止相似供体细胞之间的交配；接合过程中的DNA切口和转移；以及这些功能表达的调控。本综述是F转移区域中发现的产物和其他特征的汇编，也是对它们在接合中作用的讨论。虽然F转移的遗传学已被广泛描述，但接合机制却难以捉摸，很大程度上是因为菌毛表达水平低以及F质粒转移所需的众多包膜成分。然而，分子遗传学技术的出现最近已取得了相当大的进展。提供F转移区域已知特性的这一综述，希望它将为未来与其他接合系统进行比较形成有用的基础。
