Major capsid protein that self-associates to form hexamers, building most of the capsid in association with pentons made of the capsid vertex protein and one dodecamer of the portal protein. The major capsid protein self-associates to form 160 hexamers, building most of the T=13 laevo capsid. Folding of major capsid protein requires the assistance of two chaperones, the host chaperone groL acting with the phage encoded gp23-specific chaperone, gp31. The capsid also contains two nonessential outer capsid proteins, Hoc and Soc, which decorate the capsid surface. Through binding to adjacent gp23 subunits, Soc reinforces the capsid structure. Homohexamer. Interacts with the portal protein. Interacts with the capsid vertex protein that forms pentamers. Interacts with hoc; one hoc molecule associates with each capsid hexamer. Interacts with soc; this interaction reinforces the capsid structure. A total of 960 subunits of the major capsid protein forms the 160 hexamers. Part of the capsid icosahedric shell of the immature virion. The capsid is made of 930 copies arranged as 160 hexamers. Part of the capsid icosahedric shell of the mature virion. The capsid is made of 930 copies arranged as 160 hexamers. A proteolytic cleavage gives rise to the mature major capsid protein during virus maturation. Belongs to the T4 phage capsid protein family.