Fig 7.

Two models of pilus assembly and functions of the PilA isoforms. The short and long isoforms are depicted in green and blue, respectively. Both isoforms are shown cleaved after glycine −1 once they reach the inner membrane (I.M.), generating identical mature proteins. Model I (right) suggests that the mature PilA derived from the short PilA isoform remains intracellular and forms the base of the pilus fiber anchoring the long-isoform-derived PilA in the cell membrane. Model II (left) suggests that secreted PilA is derived from both preprotein isoforms, and long- and short-isoform-derived PilA proteins are assembled into the intra- and extracellular regions of the pilus fiber. O.M., outer membrane.