Chlamydomonas reinhardtiicDNAs upregulated in low-CO₂conditions: expression and analyses

Unicellular algae acquire the ability to raise their internal CO 2 concentrations under low-CO 2 conditions because of the presence of a CO 2 concentrating mechanism (CCM). In Chlamydomonas reinhardtii, this mechanism is induced when cells grown in high-CO 2 conditions are switched to low-CO 2 conditions. To elucidate the genes and proteins involved in this mechanism, we constructed a cDNA library from low CO 2 adapted cells and differentially screened the library for cDNAs upregulated under low-CO 2 conditions. Earlier studies identified six classes of clones specific to low CO 2 adapting cells. To identify other genes and proteins playing a role in this mechanism, we have systematically characterized the cDNA clones that appear to be upregulated by low-CO 2 adaptation but do not cross-hybridize with the six previously identified classes. We identified seven new classes of clones that are distinctly upregulated in low-CO 2 conditions. These clones were checked by Northern analyses, sequencing, and homology studies. One class of clone represents a novel gene, lci 3. We report on the seven classes of clones and the characterization of lci 3.