Regulation of the Synthesis of Ribulose-1,5-Bisphosphate Carboxylase and Its Subunits in the Flagellate Chlorogonium elongatum. Different Levels of Translatable Messenger RNAs for the Large and the Small Subunits in Autotrophic and Heterotrophic Cells as Determined by Immunological Techniques

Abstract

Poly(A)-rich and poly(A)-free RNA were isolated from autotrophic and heterotrophic cells of the phytoflagellate C. elongatum and translated in an mRNA-depleted reticulocyte lysate system. Immunoprecipitation methods were improved to detect large and small subunits of the chloroplast enzyme ribulose-1,5-bisphosphate carboxylase synthesized in vitro. Large-subunit polypeptides were the translation products of poly(A)-free RNA having the same MW as large subunits made in vivo. Small-subunit polypeptides were synthesized when poly(A)-rich RNA was used as a template. They were made in vitro as a precursor, with an MW .apprx. 6000 larger than mature small subunits. Cells growing heterotrophically in the dark with acetate are provided with lower levels of mRNA activities for the large and the small subunits than autotrophically cultured cells. Synthesis of large and small subunits is at least partially controlled by the amounts of translatable mRNA.