Auxiliary factor required, together with HCF244, for the biogenesis of photosystem II (PSII), especially for the synthesis of the reaction center proteins (e.g. D1), via the regulation of the corresponding mRNA (e.g. psbA) translation initiation (ribosomal loading) and stabilization. Component of a high molecular weight complex containing psbA mRNA, OHP1, OHP2 and HCF244, and PSII core proteins D1/D2, HCF136 and HCF173 (PubMed:17435084, PubMed:23027666, PubMed:29438089). Interacts with LPE1 (PubMed:29891689). Predominantly present at thylakoid membranes. Impaired photoautotrophy (PubMed:17435084, PubMed:23027666). Seedling lethal (PubMed:23027666). High chlorophyll fluorescence phenotype and severely affected photosystem II (PSII) subunits accumulation associated with a drastically decreased synthesis of the reaction center protein D1 due to a reduced translation initiation (ribosomal loading) of the corresponding psbA mRNA (PubMed:17435084, PubMed:23027666, PubMed:30844105). Plants lacking both HCF173 and HCF244 display stronger PSII defects (PubMed:23027666). Belongs to the NmrA-type oxidoreductase family.