Transfer of the F factor

Transfer of the Hfr F+ factor

Excision of the F+ factor also occurs

spontaneously at low frequency.

Begin with Hfr cell containing F+.

Small section of host chromosome also

may be excised, creating an F’

plasmid.

F’ plasmid is named for the gene it

carries, e.g., F’ (lac)

Interrupted

mating

experiment

F- bacteria

2 Conjugation F plasmid

Mating Bridge

F+ bacteria

F plasmid

2 Conjugation

F- bacteria

F plasmid

F+ bacteria

F plasmid

Mating Bridge

Genetic map-results of interrupted E. coli mating experiment

F+ factor (fertility factor)- a sophisticated plasmid

OriT, Origin of transfer

insertion sequences,

genes for own replication,

genes for own transfer

Conjugation converts an F- to F+. Original F+ remains F+

Note: No host genes (in blue) transferred from F+ to F-

To transfer host genes, need an Hfr strain

(high frequency)

Homologous

Recombination

here

One cell will have one or another of these

F+ to Hfr relative low frequency (~few %).

X-ray induces Hfrs. Why?,

Using an Hfr for gene transfer