Regulation and Physiological Role of the DAS1 Gene, Encoding Dihydroxyacetone Synthase, in the Methylotrophic Yeast Candida boidinii

The physiological role of dihydroxyacetone synthase (DHAS) in Candida boidinii was evaluated at the molecular level. The DAS1 gene, encoding DHAS, was cloned from the host genome, and regulation of its expression by various carbon and nitrogen sources was analyzed. Western and Northern analyses revealed that DAS1 expression was regulated mainly at the mRNA level. The regulatory pattern of DHAS was similar to that of alcohol oxidase but distinct from that of two other enzymes in the formaldehyde dissimilation pathway, glutathione-dependent formaldehyde dehydrogenase and formate dehydrogenase. The DAS1 gene was disrupted in one step in the host genome (das1Δ strain), and the growth of the das1Δ strain in various carbon and nitrogen sources was compared with that of the wild-type strain. The das1Δ strain had completely lost the ability to grow on methanol, while the strain with a disruption of the formate dehydrogenase gene could survive (Y. Sakai et al., J. Bacteriol. 179:4480–4485, 1997). These and other experiments (e.g., those to determine the expression of the gene and the growth ability of the das1Δ strain on media containing methylamine or choline as a nitrogen source) suggested that DAS1 is involved in assimilation rather than dissimilation or detoxification of formaldehyde in the cells.