What is the selection for transfer of the fplasmid from the

What is the selection for transfer of the f-plasmid from the donor?

Solution

Ans:

Transfer of genes from an Hfr into an F- recipient cell requires the recA gene product because the incoming genes need to be inherited by homologous recombination. This two cross-over event is mediated by the recA gene. Since the incoming genes are on an unstable linear fragment of DNA, if the genes aren\'t recombined into the chromosome by RecA, then the DNA will be degraded by exonucleases.

Transfer of an F\' can occur in a recA mutant because the F\' does not need to recombine with the recipient chromosome in order to be stably inherited. The final step in the transfer of an F\' is a site-specific recombination event between the first and second copy of oriT to be transferred into the recipient cell. This single cross-over event is mediated by one of the tra genes encoded on the F\' plasmid, and is independant of recA. This site-specific recombination event occurs at the conjugal bridge between the two cells, and results in a new F\' plasmid in the recipient cell that may complement mutant genes on the recipient chromosome, if the wild-type copies are present on the F\'.