The T-pilus of Agrobacterium tumefaciens.

T-pilus biogenesis uses a conserved transmembrane nucleoprotein- and protein-transport apparatus for the transport of cyclic T-pilin subunits to the Agrobacterium cell surface. T-pilin subunits are processed from full-length VirB2 pro-pilin into a cyclized peptide, a rapid reaction that is Agrobacterium specific and can occur in the absence of Ti-plasmid genes.