Identification of a novel C20-elongase gene from the marine microalgae Pavlova viridis and its expression in Escherichia coli.

Pavlova viridis, a species of a unicellular marine microalgae, is rich in the very-long-chain polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3). A new elongase gene (elkj), with high identity with a functionally characterized C20-elongase of Pavlova lutheri, was isolated via reverse transcriptase-polymerase chain reaction using the primers designed from conserved motifs and 5'/3' rapid amplification of cDNA ends. The coding region of 314 amino acids predicted a protein of 34 kDa, which contained seven transmembrane domains with its C-terminal in the cytoplasm and located in the endoplasmic reticulum. The expression of ELKJ in Escherichia coli was carried out by using green fluorescent protein as an indicator, suggesting the correct insertion in cytoplasmic membrane. Functional analysis demonstrated that elkj encoded a C20-elongase that mediated the elongation of EPA into docosapentaenoic acid (22:5n-3), confirming the two-step conversion from EPA to DHA in marine microalga.