Self assembles to form a helical capsid wrapping up the viral genomic DNA. The capsid displays a filamentous structure with a length of 760-1950 nm and a width of 6-8 nm. The virion assembly and budding take place at the host inner membrane (By similarity). Homomultimerizes. There are several thousands of this protein in the phage capsid (By similarity). prior to assembly, the major capsid protein is found associated with the bacterial host inner membrane. Belongs to the inovirus capsid protein family.