A factor required for optimal assembly of photosystem II (PSII) which acts in the early stages of PSII assembly. Also plays a role in replacement of photodamaged D1 (psbA). May interact with precursor D1 to prevent its premature processing before association with D2 (psbD) (Probable). May also play a role in chlorophyll insertion into chlorophyll-binding proteins (Probable). Increasing levels of chlorophyll precursors partially suppresses deletion of this protein, supporting the idea that Ycf48 assists YidC in synthesis of chlorophyll-binding proteins. The Ycf39-Hlip complex binds D1 at an early stage of PSII assembly along with Ycf48, ribosomes and ChlG, the last enzyme in chlorophyll biosynthesis; it may be involved in chlorophyll reuse and delivery to D1 in the initial stages of PSII assembly