The major coat protein in the capsid of filamentous bacteriophage forms a helical assembly of about 7000 identical protomers, with each protomer comprised of 46 amino acid, after the cleavage of the signal peptide. Each protomer forms a slightly curved helix that combine to form a tubular structure that encapsulates the viral DNA [1].

1: The molecular structure and structural transition of the alpha-helical capsid in filamentous bacteriophage Pf1. Welsh LC, Symmons MF, Marvin DA; Acta Crystallogr D Biol Crystallogr 2000;56:137-150. PMID:10666593

2: Phage liquid crystalline droplets form occlusive sheaths that encapsulate and protect infectious rod-shaped bacteria. Tarafder AK, von Kugelgen A, Mellul AJ, Schulze U, Aarts DGAL, Bharat TAM; Proc Natl Acad Sci U S A. 2020;117:4724-4731. PMID:32071243

3: Molecular models and structural comparisons of native and mutant class I filamentous bacteriophages Ff (fd, f1, M13), If1 and IKe. Marvin DA, Hale RD, Nave C, Helmer-Citterich M; J Mol Biol 1994;235:260-286. PMID:8289247