Fertility factor

The Fertility factor (also known as F factor or sex factor) is a bacterial DNA sequence that allows a bacterium to produce a sex pilus necessary for conjugation. It contains 20 tra (for "transfer") genes and a number of other genetic sequences responsible for incompatibility, replication, and other functions. The F factor is an episome and can exist as an independent plasmid or integrate into the bacterial cell's genome. There are several names for the possible states:


 * Hfr bacteria possess F factor integrated into the bacterial genome.


 * F+ bacteria possess F factor as a plasmid independent of the bacterial genome. The F plasmid contains only F factor DNA and no DNA from the bacterial genome.


 * F' (F-prime) bacteria possess an F plasmid that also includes some DNA taken from the bacterial genome.


 * F- bacteria do not contain F factor.

When an F+ cell conjugates with an F− cell, the result is two F+ cells, both capable of transmitting the plasmid further by conjugation. In the case of Hfr, the result is one Hfr and one F− cell because there is no F plasmid free to be replicated and transferred to the F− cell. When F-prime plasmids are transferred to a recipient bacterial cell, they carry pieces of the donor's DNA that can become important in recombination. Bioengineers have created F plasmids that can contain inserted foreign DNA; this is called a fosmid.

F-Plasmid F-плазмида