Possible involvement of a low redox potential component(s) downstream of photosystem I in the translational regulation of the D1 subunit of the photosystem II reaction center in isolated pea chloroplasts

Accumulation of the precursor and the mature form of the D1 protein of the photosystem II reaction center in illuminated pea chloroplasts was prevented by the addition of the inhibitors atrazine, 3-(3,4-dichlorophenyl)- 1,1-dimethylurea and 3,5-dibromo-4-hydroxybenzonitrile. Under such conditions, the compensatory accumulation of two translational intermediates of the D1 protein, of 22 and 24 kDa, respectively, was induced by the addition of ATP, as also observed in darkness in the presence of ATP [Taniguchi et al. (1993) FEBS Lett. 317: 57], suggesting that the synthesis of the full-length D1 protein requires a factor that is generated by the operation of photosynthetic electron transport. The accumulation of the full- length D1 protein was induced in the light, even in the presence of atrazine, when both 2,6-dichlorophenolindophenol and ascorbate were also present and in darkness upon the addition of dithiothreitol. Moreover, reagents with a relatively low redox potential, namely, duroquinone and methylviologen, prevented the accumulation. These observations suggest that the translation of the D1 protein might be regulated at specific steps during the elongation of the polypeptide via a redox change in a component around photosystem I. Results of pre-illumination experiments indicate that the factor needed for the accumulation of D1 protein is relatively stable and retains its activity in darkness after exposure to light.