Unlike other plasmids, F factor is constitutive for transfer proteins due to a mutation in the gene finO.
[3][10] 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.
The finO gene of the original F plasmid (in E. coli K12) is interrupted by an IS3 insertion, resulting in constitutive tra operon expression.
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.