Conjugation

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Schematic diagram of bacterial conjugation. 1 - Donor cell produces pilus. 2 - Pilus attaches to recipient cell, brings the two cells together. 3 - The mobile plasmid is nicked and a single strand of DNA is then transferred to the recipient cell. 4 - Both cells recircularize their plasmids, synthesize second strands, and reproduce pili; both cells are now viable donors. Image courtesy of Wikipedia

Bacterial conjugation is the transfer of genetic material between two bacterial cell via direct cell-to-cell contact. Although often incorrectly characterized as the bacterial equivalent of mating, in fact it is simply the transfer of genetic material from a donor cell to a recipient cell. Bacterial conjugation is also known as a "type IV secretion system".

This behaviour is characterized by the presence of a specialized plasmid (small, circular piece of transferrable DNA most often found within bacteria) known as a conjugative plasmid. The conjugative plasmid holds a distinct and specialized set of coding regions including the following

  • OriT (Origin of Transfer): Unlike other plasmids, the conjugative plasmid has its own origin of transfer nic region. This is a specialized portion of the genome where one of the two strands of the circular plasmid DNA is cut to allow for rolling circle replication of the plasmid containing the OriT region into a recipient cell. During rolling circle replication, the cut end of one strand is inserted into the recipient cell while recipient polymerases construct the complementary strand back into a circular piece of DNA.
  • TraJ (Transfer genes): The activation of this gene sets off a cascade of other plasmid genes (and thus corresponding protein expressions) which act in concert to form "mating" characteristics in the host bacterial cell. Such salient characteristics include:
    • growth of a pilus--a long whip-like apparatus used to hook the two cells together
    • fusion of the outer membranes to allow for transfer of genetic material
    • formation of "surface exclusion proteins" which prevents the cell containing the conjugative plasmid from mating with other conjugative plasmids of its type

Two of the most well-studied and characterized types of conjugative plasmids are types "F" (from the F plasmid) and "R". The employed nomenclature for conjugative plasmid genes is the gene name first with the type afterwards. For example, the "TraJr" or "TraJR" gene denotes the "TraJ" gene of the "R" type conjugative plasmid.

Note it was previously believed that transfer of genetic material occurred via the pilus itself; now, most think that the transfer of genetic material occurs via a separate direct channel between the two cells.



More...
-?-NameTypeDescriptionLength
  BBa_I714000ConjugationR388 oriT ( transfer origin of E.coli IncW group R388 plasmid)402
  BBa_I714003Conjugationminimum oriT of plasmid R64 ( origin of transfer, R64 is IncI-1 )83
1WBBa_I714030ConjugationOriT-F (Origin of Transfer for the F-plasmid nic region)355
1WBBa_I714031ConjugationOriT-R (Origin of Transfer for the R751-plasmid nic region) 278
AWBBa_I714032ConjugationOriT-S (Origin of Transfer for the pSC101-plasmid nic region) 131
   BBa_J01000CodingTraJF controls conjugative transfer in F plasmid690
1  BBa_J01001CodingTraJr protein (controls conjugative transfer in RP4 plasmid)378
1WBBa_J01002ConjugationOriT-F (Origin of Transfer for the F-plasmid nic region)365
1  BBa_J01003ConjugationOriT-R (Origin of transfer for the R-plasmid nic region)371
 WBBa_J01077PlasmidF plasmid (x-OriT, x-TraJ) 
 WBBa_J01078PlasmidR plasmid (x-OriT, x-TraJ) 
  BBa_J23046Conjugationput in later - SIL strain 
AWBBa_J61030Composite[OriTr][R6K]785
   BBa_K1053123ConjugationSplit EYFP N-terminal domain fused with HTLV-1 Rex peptide606
   BBa_K1053124ConjugationSplit EYFP C-terminal domain fused with λN peptide297
A BBa_K109550CodingBacterial conjugative regulator KorA306
A  BBa_K109551CodingTrbA transcription factor for the Tra2 operon in incP alpha conjugation366
A  BBa_K125320ConjugationOriT-RP4 (Origin of transfer for the RP4 plasmid)99
A  BBa_K125350ConjugationoriTr with lac promoter and lacZ979
A  BBa_K125360ConjugationoriT with lac promoter and lacZ707
AWBBa_K150006ConjugationoriT471
  BBa_K175000CodingtrbC (pilin) of IncP beta R751 plasmid468
AWBBa_K175001CodingtrbK (entry exclusion) of IncP beta R751 plasmid231
  BBa_K188777Conjugationaka879
  BBa_K188778Conjugationas864
   BBa_K543016ConjugationBacteriophage Lysis Cassette S105, R, and Rz under Tet promoter (conjugative)1838
   BBa_K543020ConjugationOriTr-GFP1254
   BBa_K543030Conjugation[I714030][J23066][I714030] (Constitutive expression)1105
   BBa_K543032Conjugationassay system of killing by conjugation3615
 WBBa_K640002ConjugationoriT - Interspecies origin of transfer260
 WBBa_K640004ConjugationDevice for conjugation of plasmids from E. coli to pseudomonas642
 WBBa_K640005ConjugationDevice for conjugating plasmids from E. coli to pseudomonas753
 WBBa_K808028SignallingPhoA: signal sequence for peri plasmic expression63
 WBBa_K873003Conjugationconjugative transfer of RFG1302
  BBa_M1355ConjugationRS1720
  BBa_M1356ConjugationRS2709


YifanYangPhoto.jpg MingzhiQuPhoto.jpg Yifan Yang, Mingzhi Qu and the 2007 Peking Yniveristy iGEM team designed the parts BBa_I714000, BBa_I714003, BBa_I714030, BBa_I714031 and BBa_I714032. IGEM2005group.jpg The 2005 Berkeley iGEM team designed the parts BBa_J01000-BBa_J01003 and BBa_J01077-BBa_J01078.
JCA Photo.png Chris Anderson and the 2006 Berkeley iGEM team design the parts BBa_J23046. IngridSwansonPhoto.jpg Ingrid Swanson and the 2008 University of Washington iGEM team designed the parts BBa_K109550 and BBa_K109551. MargaretRuzickiPhoto.jpg Margaret Ruzicki and the 2008 University of Hawaii iGEM team designed the parts Part:BBa_K125320, Part:BBa_K125350, and Part:BBa_K125360.

References