Analysis of the sequence and gene products of the transfer region of the F sex factor

Abstract

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.

Bioinformatic Analysis of the Campylobacter jejuni Type VI Secretion System and Effector Prediction

“…Of the T6SS-negative genomes, 5 out of the 60 were found to contain CJIE3 (Supplementary Table 11). The N-terminus of TraG is required for F pilus assembly; a long filament mediating the conjugative transfer of genetic material (Frost et al, 1994). Homologues of TraG and transfer coupling protein VirD4, a component of the Agrobacterium tumefaciens Type IVa secretion system (T4SSa), have been previously identified in the chromosomes of C. jejuni 81-176 and ATCC 43431, as well as in plasmids pCC31 and pTet (Batchelor et al, 2004;Poly et al, 2005;Chandran Darbari and Waksman, 2015).…”

Genomic network analysis of environmental and livestock F-type plasmid populations

“…Most plasmids were predicted to be conjugative (516/726), with a smaller number predicted to be mobilisable (39/726) or non-mobilisable (171/726) (see “Materials and methods”). All plasmids predicted to be conjugative were larger than 42 kbp, consistent with the complete tra region of F-type plasmids being approximately 33 kbp [ 30 ]. We found 24 different replicons across all plasmids, including 11 in unspecified gene clusters, present in 52 different combinations or ‘replicon haplotypes’ (Table S2 ).…”

Inter- and Intramolecular Determinants of the Specificity of Single-Stranded DNA Binding and Cleavage by the F Factor Relaxase

“…The TraI36 variant Y16F (TraI36(Y16F)) was crystallized with a bound ssDNA oligonucleotide (5#-TGGGGTGTĜ GTGCTTTTGGTGG-3#) corresponding to the complement of bases 127-148 of the F plasmid oriT sequence (Genbank accession number U01159 [Frost et al, 1994]). The sequence begins 8 bases 5# to nic (denoted by "^"), the site of specific ssDNA cleavage by TraI (Matson and Morton, 1991;Reygers et al, 1991).…”