In-vivo and in-vitro synthesis of photosynthetic fructose-1,6-bisphosphatase from pea (Pisum sativum L.).

Etiolated pea (Pisum sativum L. cv. Lincoln) seedlings do not show any capability for the biosynthesis of chloroplast fructose-1,6-bisphosphatase (FBPase), but the rate of biosynthesis of the increases with the pre-illumination time. This light-induced FBPase synthesis appears to be regulated at the transcriptional level, the response of young leaves being greater than that of mature ones. In-vivo labelling experiments demonstrated by immunoprecipitation, followed by sodium dodecyl sulfate electrophoresis and fluorography, the presence of a 49-kilodalton (kDa) band which corresponds to the mature FBPase subunit. In-vitro translation experiments with a wheat-germ synthesizing system and polyadenylated mRNA isolated from illuminated young pea seedlings have demonstrated the appearance of a 59-kDa labelled band corresponding to the precursor of the FBPase basic subunit. When intact pea chloroplasts were added to the above in-vitro incubation mixture, a labelled 49-kDa subunit similar to that of the in-vivo experiments appeared in the organelle under illumination. From these results we can conclude that a 10-kDa transit peptide bound to the translated pea FBPase subunit exists in the cytosol; this transit peptide is lost during passage through the chloroplast envelope, leaving the mature subunit inside the organelle.