Characteristics of the gene that encodes acetyl-CoA carboxylase in the diatom Cyclotella cryptica

Efforts are currently under way in several laboratories to develop renewable fuels from biological sources. Our group conducts research involving the production of lipid-derived "biodiesel" fuel from microscopic algae. Lipid accumulation in algae typically occurs during periods of environmental stress, including growth under nutrient-deficient conditions. Biochemical studies have suggested that acetyl-CoA carboxylase (ACCase), a biotin-containing enzyme that catalyzes an early step in fatty acid biosynthesis, may be involved in the control of this lipid accumulation process. Therefore, it may be possible to enhance lipid production rates by increasing the activity of this enzyme via genetic engineering. As a first step toward this objective, we have cloned the gene that encodes ACCase from the eukaryotic alga Cyclotella cryptica. This is the first time that this gene has been isolated from a photosynthetic organism. The amino acid sequence of ACCase deduced from this gene exhibits a high degree of similarity to the sequences of animal and yeast ACCases in the biotin carboxylase and carboxyltransferase domains, but less similarity exists in the biotin carboxyl carrier protein domain. Comparison of the genomic nucleotide sequence to the sequences of cDNA clones has revealed the presence of two introns in the gene. We are currently constructing expression vectors containing this gene and developing algal transformation protocols to enable overexpression of ACCase in C. cryptica and other algal species.