Comparison of Proteins Involved in Pilus Synthesis and Mating Pair Stabilization from the Related Plasmids F and R100-1: Insights into the Mechanism of Conjugation

Abstract

F and R100-1 are closely related, derepressed, conjugative plasmids from the IncFI and IncFII incompatibility groups, respectively. Heteroduplex mapping and genetic analyses have revealed that the transfer regions are extremely similar between the two plasmids. Plasmid specificity can occur at the level of relaxosome formation, regulation, and surface exclusion between the two transfer systems. There are also differences in pilus serology, pilus-specific phage sensitivity, and requirements for OmpA and lipopolysaccharide components in the recipient cell. These phenotypic differences were exploited in this study to yield new information about the mechanism of pilus synthesis, mating pair stabilization, and surface and/or entry exclusion, which are collectively involved in mating pair formation (Mpf). The sequence of the remainder of the transfer region of R100-1 (trbA to traS) has been completed, and the complete sequence is compared to that of F. The differences between the two transfer regions include insertions and deletions, gene duplications, and mosaicism within genes, although the genes essential for Mpf are conserved in both plasmids. F+ cells carrying defined mutations in each of the Mpf genes were complemented with the homologous genes from R100-1. Our results indicate that the specificity in recipient cell recognition and entry exclusion are mediated by TraN and TraG, respectively, and not by the pilus.

Insights into organohalide respiration and the versatile catabolism of Sulfurospirillum multivorans gained from comparative genomics and physiological studies

“…This region has a 6% lower GC content than the genome average and a high percentage of ORFs, which either cannot be assigned to any function or are related to DNA binding and repair, plasmid stabilization or genetic mobilization. The genes related to genetic mobilization include several ORFs presumably encoding proteins similar to the Tra system (Anthony et al, 1999). Some single phage proteins were found in that region and an analysis with the phage finder software PHISPY (Akhter et al, 2012) revealed the presence of a putative prophage spanning the whole 150 kb region.…”

Evidence that F‐plasmid proteins TraV, TraK and TraB assemble into an envelope‐spanning structure in Escherichia coli

“…All these phenotypes are consistent with a failure of the initiation or elongation of F-pilus filaments. Anthony et al (1999) reported that traB2 and traV569 mutants could still be infected by M13K07, as measured by transduction of kanamycin resistance, albeit at reduced levels. This would suggest a failure of filament elongation, as M13 binds to the tips of F-pili.…”

F factor conjugation is a true type IV secretion system

“…Other conjugative elements which contain F-type T4SS include, besides the F factor (E. coli) [7], R100 (IncFII) [32], pED208 (IncFV; S. typhi) [39], R27 (IncHI1; S. typhi) [78], Rts1 (IncT; Proteus vulgaris) [79], R391 (IncJ; Providencia rettgeri) [80], SXT element (Vibrio cholerae) [81] and pNL1 (Novosphingomonas aromaticivorans) [82] (Fig. 1).…”

“…Some evidence is available that suggests the T4SS system of F penetrates the recipient cell. TraG F has been implicated in entry exclusion involving protein^protein interactions between TraG F and TraS F , the entry exclusion protein, located in the donor and recipient cells, respectively [32]. This suggests that TraG F is translocated into the recipient cell and interacts with TraS F to block DNA transfer.…”