Function
When an F+ cell conjugates/mates with an F− cell, the result is two F+ cells, both capable of transmitting the plasmid to other F- cells by conjugation. The F-plasmid belongs to a class of conjugative plasmids that control sexual functions of bacteria with a fertility inhibition (Fin) system. In this system, a trans-acting factor, FinO, and antisense RNAs, FinP, combine to repress the expression of the activator gene TraJ. TraJ is a transcription factor that upregulates the tra operon. The tra operon includes genes required for conjugation and plasmid transfer. This means that an F+ bacteria can always act as a donor cell. The finO gene of the original F plasmid is interrupted by an IS3 insertion, resulting in constitutive tra operon expression, in E. coli K12. F+ cells also have the surface exclusion proteins TraS and TraT on the bacterial surface. These proteins prevent secondary mating events involving plasmids belonging to the same incompatibility (Inc) group. Thus, each F+ bacterium can host only a single plasmid type of any given incompatibility group.
In the case of Hfr transfer, the resulting transconjugates are Hfr cells as well. 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 bacterial artificial chromosome.
The first DNA helicase ever described is encoded on the F-plasmid and is responsible for initiating plasmid transfer. It was originally called E. coli DNA Helicase I, but is now known as F-plasmid TraI. In addition to being a helicase, the 1756 amino acid (one of the largest in E. coli) F-plasmid TraI protein is also responsible for both specific and non-specific single-stranded DNA binding as well as catalyzing the nicking of single-stranded DNA at the origin of transfer.
Read more about this topic: Fertility Factor
Famous quotes containing the word function:
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