This family consists of several enterobacterial PilO proteins. The function of PilO is unknown although it has been suggested that it is a cytoplasmic protein in the absence of other Pil proteins, but PilO protein is translocated to the outer membrane in the presence of other Pil proteins. Alternatively, PilO protein may form a complex with other Pil protein(s). PilO has been predicted to function as a component of the pilin transport apparatus and thin-pilus basal body. This family does not seem to be related to pfam04350.