The PsbI protein, previously named the 4.8-kDa protein, is encoded by the plastome. PsbI is a universal component of PSII and is highly conserved (e.g. there is 71% amino acid identicality between the Arabidopsis and Synechocystis 6803 proteins). The protein contains 36 to 38 amino acids in most species, with molecular masses ranging between 4.1 and 4.5 kDa. Synonymes: PSII-I, PSII 4.8 kDa protein