Abstract
Chloroplast psbD and psbC genes encode a D2 and a CP43 protein of photosystem II complex, respectively. These genes are members of psbD operon with psbZ and are co-transcribed from a promoter upstream of psbD. The psbC is also transcribed from its own promoter. A striking feature of this operon is that psbD and psbC coding regions partially overlap, implying translation of downstream psbC from the polycistronic mRNA is dependent on that of upstream psbD. To examine this possibility, we carried out tobacco chloroplast in vitro translation assays. Our result indicates that translation of psbC from a dicistronic psbD-psbC mRNA was much more efficient than that from monocistronic psbC mRNA by chloroplast in vitro translation assays. In addition, translation of the psbC from the dicistronic mRNA was strongly dependent on that of the first cistron. Mechanism of translational coupling between psbD and psbC will be discussed.
