Post-transcriptional regulation by light of the biosynthesis of Euglena ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit.

In Euglena gracilis, the amounts of the mature small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) increase during cell greening, while an analysis of the transcripts, performed at different stages of chloroplast development, shows no difference in the amounts of the corresponding mRNA. Pulse-chase experiments followed by immunoprecipitation show a significant increase in the rate of synthesis of the large molecular weight precursor (which consists of a transit peptide followed by eight small subunits) beginning after 12 h of illumination. Nevertheless, its half life does not change significantly during the chloroplast development. The results presented strongly suggest that the regulation of the expression of the Rubisco small subunit occurs at the translational level.