## LSU Historical Dissertations and Theses

1998

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

#### Department

Biological Sciences

James V. Moroney

#### Abstract

A mechanism that concentrates CO$\sb2$ in cells of Chlamydomonas reinhardtii, is induced when cells are grown at low CO$\sb2$ conditions. This mechanism increases the CO$\sb2$ concentration at the site of RuBisCO, and thereby improves the efficiency of C$\rm\sb{i}$ uptake and fixation. Cells adapting to low CO$\sb2$ show significant physiological changes. Few of the genes encoding proteins needed to produce these changes have been identified. A cDNA library has been constructed from C. reinhardtii to identify genes involved in these changes. The cloning and identification of several cDNAs that are upregulated under low CO$\sb2$ conditions are reported here. The possible roles that these cDNAs play in the CO$\sb2$ concentrating mechanism are also discussed. Two cDNAs induced at low CO$\sb2$ are carbonic anhydrases. These cDNAs show homology to $\beta$ carbonic anhydrases from higher plants. The complete sequence of another cDNA, Lci 3, does not show homology to any known proteins. Increased abundance of the Lci 3 transcript suggests that it plays an important role in the CCM. Two other clones that are upregulated in low CO$\sb2$ conditions have been identified as PsaE and omega 6 desaturase. Four other cDNAs upregulated under low CO$\sb2$ conditions code for proteins found in the light harvesting complex (LHC) family. A role in the energization of the CO$\sb2$ concentrating mechanism is proposed for these proteins. Lastly, a cDNA encoding a cyclophilin has been identified. Cyclophilins are a class of proteins with a cis/trans prolyl isomerase activity. This is the first report of CO$\sb2$ concentration affecting the expression of a cyclophilin. Based on in vitro studies a role in the proper folding of some of the newly synthesized proteins induced under low CO$\sb2$ conditions is proposed for the C. reinhardtii cyclophilin.

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