title: F factor conjugation is a true type IV secretion system.
abstract: The F sex factor of Escherichia coli is a paradigm for bacterial conjugation and its transfer (tra) region represents a subset of the type IV secretion system (T4SS) family. The F tra region encodes eight of the 10 highly conserved (core) gene products of T4SS including TraAF (pilin), the TraBF, -KF (secretin-like), -VF (lipoprotein) and TraCF (NTPase), -EF, -LF and TraGF (N-terminal region) which correspond to TrbCP, -IP, -GP, -HP, -EP, -JP, DP and TrbLP, respectively, of the P-type T4SS exemplified by the IncP plasmid RP4. F lacks homologs of TrbBP (NTPase) and TrbFP but contains a cluster of genes encoding proteins essential for F conjugation (TraFF, -HF, -UF, -WF, the C-terminal region of TraGF, and TrbCF) that are hallmarks of F-like T4SS. These extra genes have been implicated in phenotypes that are characteristic of F-like systems including pilus retraction and mating pair stabilization. F-like T4SS systems have been found on many conjugative plasmids and in genetic islands on bacterial chromosomes. Although few systems have been studied in detail, F-like T4SS appear to be involved in the transfer of DNA only whereas P- and I-type systems appear to transport protein or nucleoprotein complexes. This review examines the similarities and differences among the T4SS, especially F- and P-like systems, and summarizes the properties of the F transfer region gene products.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E9.
authors.forename: T D
authors.initials: TD
authors.lastname: Lawley
authors.forename: W A
authors.initials: WA
authors.lastname: Klimke
authors.forename: M J
authors.initials: MJ
authors.lastname: Gubbins
authors.forename: L S
authors.initials: LS
authors.lastname: Frost
mesh_terms: D000595:Amino Acid Sequence; D003227:Conjugation, Genetic / Q000502:physiology*; D004926:Escherichia coli / Q000235:genetics*; D005144:F Factor / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny