Chaperone required for efficient photosystem II (PSII) assembly. Binds to psbA during de novo biogenesis of PSII. Interacts with psbA, but not with psbD, petB, ALB3, LPA2 or LPA3. Is not a component of the PSII complex. Pale-green phenotype and greatly reduced growth. Disturbed thylakoid membrane systems. Accumulates even in dark-grown seedlings. An article reported a lack of interaction with LPA2; however, this paper was later retracted.