One of the components of the core complex of photosystem II (PSII). PSII is a light-driven water:plastoquinone oxidoreductase that uses light energy to abstract electrons from H(2)O, generating O(2) and a proton gradient subsequently used for ATP formation. It consists of a core antenna complex that captures photons, and an electron transfer chain that converts photonic excitation into a charge separation. PSII binds multiple chlorophylls, carotenoids and specific lipids. Cyanobacterial PSII is composed of 1 copy each of membrane proteins PsbA, PsbB, PsbC, PsbD, PsbE, PsbF, PsbH, PsbI, PsbJ, PsbK, PsbL, PsbM, PsbT, PsbX, PsbY, PsbZ, Ycf12, at least 3 peripheral proteins PsbO, PsbU, PsbV and a large number of cofactors. It forms dimeric complexes. Suggests the protein is 1 residue shorter at the N-terminus and N-formylated. No change in growth rate or oxygen evolution under standard growth conditions (50 umol photons/m(2)/s and 45 degrees Celsius). Dimeric PSII less stable upon isolation, soluble protein Psb28 associates substoichiometrically with PSII. Only the D1 protein translated from the psbA2 or psbA3 gene is found in PSII. Belongs to the PsbJ family.