Conjugation involves a donor cell, which contains a particular type of conjugative plasmid, and a recipient cell, which does not The genes that control conjugation are contained in the tra region of the plasmid(see Section 9. 8 in your text). Many genes in the tra region have to do with the synthesis of a surface structure, the sex pilus. Only donor cells have these pili, The pili make specific contact with a receptor on the recipient and then retract, pulling the two cells together. The contacts between the donor and recipient cells then become stabilized probably from fusion of the outer membranes, and the dna is then transferred from one cell to another
Conjugation involves a donor cell, which contains a particular type of conjugative plasmid, and a recipient cell, which does not. The genes that control conjugation are contained in the tra region of the plasmid (see Section 9.8 in your text ). Many genes in the tra region have to do with the synthesis of a surface structure, the sex pilus . Only donor cells have these pili, The pili make specific contact with a receptor on the recipient and then retract, pulling the two cells together. The contacts between the donor and recipient cells then become stabilized, probably from fusion of the outer membranes, and the DNA is then transferred from one cell to another
Conjugation and Chromosome mobilization F+ and F-strains Ft strains: cells possessing an unintegrated F plasmid. F- strains: cells which can act as recipients for Ft or Hfr, F- strains lack f plasmid. F plasmid provides its host cell with: ability to synthesize the f pilus mobilization of dna for transfer to another cell alteration of surface receptors so that the cell is no longer able to behave as a recipient in conjugation
Conjugation and Chromosome Mobilization: F+ and F- strains • F+ strains: cells possessing an unintegrated F plasmid. • Fstrains: cells which can act as recipients for F+ or Hfr, Fstrains lack F plasmid. • F plasmid provides its host cell with: – ability to synthesize the F pilus – mobilization of DNA for transfer to another cell – alteration of surface receptors so that the cell is no longer able to behave as a recipient in conjugation
E Integration of an F plasmid into the chromosome with the formation of an fr is elements are the sites of insertion B Recombination ho omolo 八 pro lac pro A C B lac
Integration of an F plasmid into the chromosome with the formation of an Hfr. IS elements are the sites of insertion. homology
D Dro Hfr strain B Hfr strains lac arise as a le result of the Integration Transfer to F re of the f ys plasmid into E the chromosome leu man cys
Hfr strain • Hfr strains arise as a result of the integration of the F plasmid into the chromosome
Important Concept: F plasmids Integrated F plasmids may be occasionally excised from the chromosome and bring some chromosomal genes with itself into the liberated f plasmid F-mediated transfer resembles specialized transduction in that only a restricted group of chromosomal genes can be transferred
Important Concept: F’ plasmids • Integrated F plasmids may be occasionally excised from the chromosome and bring some chromosomal genes with itself into the liberated F plasmid. • F’-mediated transfer resembles specialized transduction in that only a restricted group of chromosomal genes can be transferred