Abstract
Carbon-concentrating mechanism (CCM) is widespread among aquatic photosynthetic organisms, and facilitates the rate of photosynthesis under CO2 limiting conditions. The CCM of a green alga, Chlamydomonas reinhardtii, is mainly regulated by CCM1/CIA5, which regulates almost all CO2-responsive genes and thus functions as the master regulator of CCM. Gel-filtration chromatography analysis revealed that CCM1 forms a high-molecular-weight complex with unknown protein(s). In order to identify factor(s) interacting with CCM1, the CCM1 complex was purified from transgenic cells expressing FLAG-tagged CCM1 fusion protein by affinity chromatography, digested in solution, and then analyzed by LC-MS/MS. In addition to previously identified CBP1 (CCM1-binding protein 1), other candidate CCM1-interacting proteins were newly identified in the fraction of the CCM1 complex. Furthermore, three phosphorylated sites were identified in the polypeptides derived from CCM1.
