Two mutants of Chlamydomonas reinhardtii, mf1 and mf2, characterized by a marked reduction in their phosphatidylglycerol content together with a complete loss in its Δ³‐trans hexadecenoic acid‐containing form, also lost photosystem II (PSII) activity. Genetic analysis of crosses between mf2 and wild‐type strains shows a strict cosegregation of the PSII and lipid deficiencies, while phenotypic analysis of phototrophic revertant strains suggests that one single nuclear mutation is responsible for the pleiotropic phenotype of the mutants. The nearly complete absence of PSII core is due to a severely decreased synthesis of two subunits, D1 and apoCP47, which is not due to a decrease in translation initiation. Trace amounts of PSII cores that were detected in the mutants did not associate with the light‐harvesting chlorophyll a/b‐binding protein antenna (LHCII). We discuss the possible role of phosphatidylglycerol in the coupled process of cotranslational insertion and assembly of PSII core subunits.