It contains the molecular characterization of a new gene encoding zinc-finger regulatory protein which transfers signals from a putative CO2 sensor to genes for carbon concentrating mechanisms (CCM) in a green algae, Chlamydomonas reihnardtii. In this field, there has been no study dealing with components of the CO2 sensory system which regulates CCM in photosynthetic organisms. This work is the first step to elucidate components for eukaryotic CCM, such as bicarbonate or CO2 transporters as well as CO2 signal transduction in organisms.

In photosynthetic organisms including higher plants and cyanobacteria, it has not been known what kinds of regulatory elements are operating in the cells to switch on or shut off the CO2 concentrating mechanisms. The gene tagging technique was shown to be useful in isolating genes in eukaryotic photosynthetic organism.

So far, many high-CO2 requiring mutants have been isolated. Among them, the cia-5 mutant isolated by UV mutagenesis was assumed to be regulatory mutant for CCM. We have independently isolated new CO2-requiring mutants by gene tagging using Nit1 (Nia1) gene. One of our high-CO2 requiring mutants C16 looked like the cia-5 mutant from the physiological point of view, and finally we made clear that the gene impaired in the cia-5 was CCM1 as in the case of C16.