Functional analysis of very long-chain fatty acid elongase gene, HpELO2, in the methylotrophic yeast Hansenula polymorpha
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We describe the cloning and functional characterization of the fatty acid elongase gene HpELO2, a homologue of the HpELO1 gene required for the production of C24:0 in the yeast Hansenula polymorpha. The open reading frame (ORF) of HpELO2 consists of 1,035 bp, encoding 344 amino acids, sharing about 65% identity with that of Saccharomyces cerevisiae Elo2. Expression of HpELO2 rescued the lethality of the S. cerevisiae elo2Δ elo3Δ double disruptant. An accumulation of C18:0 and a significant increase and decrease in the levels of C24:0 and C26:0, respectively, were observed in the Hpelo2Δ disruptant. These results supported an idea that HpELO2 encodes a fatty acid elongase involved in the elongation of C18:0 to very long-chain fatty acids. The Hpelo1Δ Hpelo2Δ double disruption was nonviable, suggesting that HpELO1 and HpELO2 are the only two genes necessary for the biosynthesis in H. polymorpha. Interestingly, transcription of HpELO2 and HpELO1 were found to be transiently up-regulated by exogenous long-chain fatty acids; however, this up-regulation was not observed with HpELO1 and HpELO2 genes driven by the constitutively expressed promoter of the HpACT gene, suggesting that exogenous fatty acids specifically trigger the transcriptional induction of HpELO1 and HpELO2 through their promoter regions.