Cell-cell interactions in conjugating Escherichia coli: purification of F pili with biological activity.

A mutant of the F sex factor has been isolated that produces more F pili per cell than does the wild-type F factor. F pili have been purified in milligram amounts from cells carrying either the mutant or the wild-type sex factor. The technique described yields F pili of up to 99% purity that can specifically bind to Escherichia coli cells and that bind to and reversibly inactivate male-specific bacteriophages. The F pilin subunit has a molecular weight of 10,750 and purified F pili have a buoyant density of 1,200 g/cm3.