The Putative Zinc-binding Domains of the Regulatory Factor CCM1 Are Indispensable for Low CO₂ Stress Responses in Chlamydomonas reinhardtii

Abstract

In CO₂-limiting stress conditions, aquatic photosynthetic organisms induce active uptake systems for inorganic carbon (Ci) that enable the accumulation of Ci within the cell (Carbon-Concentrating Mechanism: CCM). In a green alga, Chlamydomonas reinhardtii, the regulatory factor CCM1 (CIA5) is indispensable for induction of the CCM. The CCM1 has two putative zinc-finger domains in its N-terminal region. Considering the fact that the mutant cia5, which has a H54Y point mutation in CCM1, does not induce the CCM under the Ci-limiting stress conditions, the putative zinc-fingers were considered to be indispensable for the function of CCM1. In order to analysis the zinc-binding activity of the putative zinc-binding site, the N-terminal region of the CCM1 were fused with GST-tag and subjected to atomic absorption analysis. We discuss about the importance of the zinc binding for the induction of CCM.