In Chlamydomonas reinhardtii the oxygen evolving enhancer protein 1 (OEE1), which is part of the oxygen evolving complex of photosystem II (PS II), is coded for by a single nuclear gene (psb1). The nuclear mutant FuD44 specifically lacks the OEE1 polypeptide and is completely deficient in photosynthetic oxygen evolution. In this mutant a 5 kb DNA insertion into the 5′ region of the psb1 gene results in the complete absence of OEE1 mRNA and protein. A revertant, FuD44‐R 2, which is capable of 30% of the photosynthetic oxygen evolution of wild‐type cells, has lost 4 kb of the 5 kb DNA insert, and accumulates both OEE1 mRNA and protein, although at levels somewhat less than those of wild‐type cells. Absence of the OEE1 protein in the FuD44 mutant does not affect the accumulation of other nuclear encoded PS II peripheral polypeptides. OEE1 absence does, however, result in a more rapid turnover of the chloroplast encoded PS II core polypeptides, thus resulting in a substantial deficiency of PS II core polypeptides in FuD44 cells. These PS II core proteins again accumulate in revertant FuD44‐R2 cells.