The F-plasmid is an example found in the bacteria Escherichia coli. It contains genes that enable the plasmid to be transferred between cells. The cells which contain the F-plasmid are F+ and the cells that don't are F-.
The transfer of the F-plasmid from one cell to another is helped by a pilus - a tubelike structure that makes the contact between the F+ and F- cell. The joining of the cells is called conjugation and the plasmids transferred are called conjugative plasmids .