'''Bacterial conjugation''' is the often regarded as the [[bacterium|bacteria]]l equivalent of [[sexual reproduction]] or [[mating]]; however it is not actually sexual as it does not involve the fusing of [[gamete]]s and the creation of a [[zygote]], it is merely the exchange of genetic information. In order to perform conjugation, one of the bacteria has to carry an '''F-[[plasmid]]''', the other one must not.
The F-plasmid (also called F-factor) is an [[episome]] (a plasmid that can integrate itself into the bacterial [[chromosome]] by [[genetic recombination]]) of about 100 kb (kilo [[base pair]]s) length. It carries its own [[origin of replication]], called ''oriV''. There can only be one copy of the F-plasmid in a bacterium (which is then called ''F-positive''), either free or integrated.
Among other genetic information, the F-plasmid carries a ''tra'' and a ''trb'' [[locus]], which together are about 33 kb long and consist of about 40 [[gene]]s. The ''tra'' locus includes the ''pilin'' gene and controlling genes, which together form [[pilus|pili]] on the cell surface, polymeric [[protein]]s that can attach themselves to the surface of ''F-negative'' bacteria and initiate the mating. The pili themselves do not seem to be the structures through which the actual exchange of DNA takes place; rather, some proteins coded in the ''tra'' or ''trb'' loci seem to open a channel between the bacteria.
The transfer of DNA always runs from the F-positive towards the F-negative bacterium.
*If the F-plasmid is free, a [[nick (DNA)|nick]] is produced in one of the circular DNA strands of the plasmid. Then, the single-stranded DNA of the nicked strand is inserted into the recipiane bacterium (5'-end first). The now single-stranded plasmid is filled up with a complementary strand by a [[rolling cycle]] mechanism.
*If the F-plasmid is integrated, the transferred DNA consists of the F-plasmid sequence plus an amount of chomosomal DNA from the donor bacterium. The amount of chromosomal DNA that is transferred depends on how long the bacteria hold contact; the transfer of the whole bacterial chromosome would take about 100 minutes. The transferred DNA can be integrated into the recipients DNA by recombination. Bacteria with an integrated F-plasmid do recombine unusually often, which is why they are also called '''Hfr-'''(high frequency recombination-)'''strains'''.
==See also ==
*[[biology]]
*[[genetics]]
*[[plasmid]]
[[Category:Molecular biology]]
[[Category:Biotechnology]]
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