Light-dependent D1 protein synthesis and translocation is regulated by reaction center II. Reaction center II serves as an acceptor for the D1 precursor.

Light induces an irreversible modification of the photosystem II reaction center (RCII) affecting specifically one of its major components, the D1 protein (Ohad, I., Adir, N., Koike, H., Kyle, D. J., and Inoue, Y. I. (1990) J. Biol. Chem. 265, 1972-1979) which is degraded and replaced continuously (turnover). The turnover rate of D1 is related to light intensity. Evidence is presented showing that RCII translocates from the site of damage in the grana (appressed) domain of the chloroplast membranes to unappressed membrane domains where the D1 precursor protein (pD1) is translated and becomes integrated into RCII. Several forms of RCII (a, a*, and b) were identified on the basis of their electrophoretic mobility. pD1 was found only in the a and b forms in the unappressed membranes. Processing of pD1 occurs after its integration into RCII. Mature D1 appeared mostly in the a form of RCII and following its translocation to the appressed membrane domains also in the a* form. Thus the light intensity-dependent synthesis of D1 protein is related to the availability of modified RCII which serves as an acceptor for pD1. The shuttling of RCII between the two membrane domains may represent a control mechanism of thylakoid membrane protein synthesis.