SexPilus

SexPilus refers to the sex pilus, a long, thin filament on the surface of many Gram-negative bacteria that mediates conjugation, a form of horizontal gene transfer. The best-known example is the F pilus encoded by the F plasmid in Escherichia coli, but related structures occur in other plasmids and chromosomal regions. SexPili are composed mainly of polymerized pilin subunits and extend from the cell envelope. Their assembly is driven by a specialized secretion system, often categorized as a type IV pilus assembly and secretion system; extension is powered by ATPases such as PilB and retraction by PilT, enabling the pilus to attach to a recipient cell and then pull the cells into proximity.

During conjugation, a relaxase-nicked plasmid DNA strand is transferred through a mating-pair formation channel, a type IV secretion system, into the recipient cell. After transfer, synthesis of the complementary strand converts the recipient into a transconjugant. The pilus itself is thought to facilitate contact and may also act to stabilize the mating pair during DNA transfer.

SexPili are common to many bacteria, including Enterobacteriaceae and Pseudomonas and others, and they play a major role in disseminating plasmids that carry accessory traits such as antibiotic resistance or virulence factors. In laboratory settings, conjugation via sex pili is a standard method for studying genetic exchange and plasmid biology.