Bacteriophage F1

Bacteriophage F1 is structurally classified as a class I filamentous phage, and is closely related to the other Ff phages, such as M13 and phage fd. Phage f1 is a filamentous (rod-shaped) ssDNA phage, with a molecular mass of about 1.6×107 Da; by weight it is 11.3 percent DNA. The flexible phages are about 850 nm long and 4.3 or 6.3 nm wide. The thousands of identical major coat proteins that make up the sheath are arranged in a fishcale-like α-helix. The ends of the filament are sealed with protein caps; the blunt end contains 3–5 copies of each VII and IX, while the terminally extruded bead-like end contains about 5 copies each of III and VI.