TRANSLATIONAL REGULATION OF THE LARGE AND SMALL SUBUNITS OF RIBULOSE BISPHOSPHATE CARBOXYLASE OXYGENASE DURING INDUCTION OF THE CO2-CONCENTRATING MECHANISM IN CHLAMYDOMONAS-REINHARDTII

In conditions of limiting external inorganic carbon, the unicellular alga Chlamydomonas reinhardtii induces a mechanism to actively transport and accumulate inorganic carbon within the cell. A high internal inorganic carbon concentration enables the cell to photosynthesize efficiently with little oxygen inhibition, even in conditions of limiting external inorganic carbon. A correlation between limiting inorganic carbon-induced induction of the CO2-concentrating mechanism and decreased synthesis of the large and small subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase has been observed. Cells that had been transferred from elevated CO2 to limiting CO2 exhibit transient declines of label incorporation into both subunit polypeptides. We have found that this decrease in synthesis of large and small subunits results from specific and coordinated down-regulation of translation of both subunits possibly resulting, at least in part, from modification of large and small subunit transcripts.