Nuclear mutation leads to an accelerated turnover of chloroplast‐encoded 48 kd and 34.5 kd polypeptides in thylakoids lacking photosystem II

We have studied the synthesis and accumulation of a chloroplast‐encoded 48 kd chla‐reaction center protein and the 34.5 kd ‘atrazine binding’ protein in a nuclear maize mutant which fails to assemble photosystem II reaction centers. The failure of these polypeptides to accumulation in mutant thylakoids is not due to direct nuclear control over their synthesis but is rather due to their specific, accelerated turnover from the thylakoid membrane. The accelerated turnover of these polypeptides in mutant thylakoids is largely independent of illumination conditions, as accelerated turnover occurs in the dark as well as in the light. In contrast to wild type, the 48 kd and 34.5 kd polypeptides are preferentially associated with stroma, rather than grana, lamellae in mutant membranes, suggesting that turnover occurs before these polypeptides become enriched in the grana. The nucleus thus plays a role in the stabilization of these chloroplast‐encoded photosystem II reaction center polypeptides.