Entry exclusion in F-like plasmids requires intact TraG in the donor that recognizes its cognate TraS in the recipient.
The mating pair stabilization (Mps) protein of the F plasmid, TraG, is unique to F-like type IV secretion systems. TraG is a polytopic inner-membrane protein with a large C-terminal periplasmic domain that is required for piliation and Mps, whereas the N-terminal region is sufficient for pilus synthesis. The C-terminal region of TraG is thought to be cleaved by the host signal peptidase I to give a fragment called TraG* that is responsible for Mps. Using mutational analysis and cell localization studies, it was shown that TraG* is most probably an artifact caused by non-specific degradation. TraS (173 aa in F), which is involved in entry exclusion (Eex), blocks redundant conjugative DNA synthesis and transport between donor cells, suggesting that it interferes with a signalling pathway required to trigger DNA transfer. Using the F and R100 plasmids, TraG in the donor cell was found to recognize TraS in the recipient cell inner membrane, in a plasmid-specific manner. This activity mapped to aa 610-673 in F TraG, the only region that differs significantly from R100 TraG. Expression of traG or traG* in a recipient cell did not affect mating ability or Eex. These results suggest that TraG may be translocated to the recipient cell, where it contacts the inner membrane, initiating transfer, a process that is blocked by TraS.
Audette
Gerald F
GF
Department of Biological Sciences, CW-405 Biological Sciences Building, University of Alberta, Edmonton, AB T6G 2E9, Canada.
Manchak
Jan
J
Beatty
Perrin
P
Klimke
William A
WA
Frost
Laura S
LS
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D003227:Conjugation, Genetic; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D005144:F Factor / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data
D001425:Bacterial Outer Membrane Proteins; D004269:DNA, Bacterial; C088223:Eex protein, E coli; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; C073791:TraG protein, E coli