Effect of CO2 Concentration on Protein Biosynthesis and Carbonic Anhydrase Expression in Chlamydomonas reinhardtii1

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RESUMO

The effect of external inorganic carbon (Ci) concentrations on protein biosynthesis and carbonic anhydrase (CA) mRNA abundance were examined in the eukaryotic alga Chlamydomonas reinhardtii. Transfer of high CO2 (5%) grown algae to air levels of CO2 resulted in the transitory synthesis of two polypeptides of approximately 49,000 and 52,000 daltons as well as prolonged synthesis and accumulation of the 37,000 dalton CA monomer and an unidentified 20,000 dalton polypeptide. The gene coding for carbonic anhydrase was isolated from a genomic expression library and subjected to restriction endonuclease analysis. Southern blot analysis of chromosomal DNA indicates that only a single copy of the gene is present. The 2.5 kilobase DNA fragment hybridizes specifically to a 1.4 kilobase transcript in RNA isolated from air-grown cells and from cells grown on 5% CO2 that have been exposed to air levels of CO2. Maximum mRNA abundance was observed after 1 to 3 hours of exposure to air. Transfer of air-grown cells to a high CO2 environment resulted in the elimination of the CA transcript after 60 minutes of exposure. Changes in CA transcript abundance in response to external Ci concentrations occurred in the presence or absence of light.

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