Plant, Animal & Microbe Genomes X Conference

January 12-16, 2002
Town & Country Convention Center
San Diego, CA

Poster: Functional Analysis
            

FATTY ACID ACYL DESATURASE GENES OF MARINE AND FRESHWATER TELEOSTS

¹ Institute of Aquaculture, University of Stirling, Stirling, Scotland, FK9 5LA, UK.

Marine teleosts, unlike their freshwater counterparts, have a repressed ability to synthesize long chain highly unsaturated fatty acids (Lc-HUFA). In competent species the delta 6 and delta 5 fatty acid desaturases are critical in the biosynthetic pathway that produces Lc-HUFA's arachidonic acid (20:4n-6), eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA). As part of our effort to understand the reason for the differences in Lc-HUFA synthesis ability between marine and freshwater teleosts we are comparing the desaturase genes of representative marine and freshwater species. The genes are being studied with a view to relating structural, and potential functional differences with different HUFA synthesis phenotypes. Among the genes so far studied is a desaturase of zebrafish (Danio rerio). The 1590 bp cDNA transcript has close sequence similarity to mammalian delta 6 desaturase genes. However, the clone encodes a novel desaturase. When expressed in Saccharomyces cerevisiae the zebrafish gene confers the ability to convert linoleic acid (18:2n-6) and alpha-linolenic acid (18:3n-3) to their corresponding delta 6 desaturase products, 18:3n-6 and 18:4n-3. In addition, it confers the ability to convert di-homo-gamma-linoleic acid (20:3n-6) and eicosatetraenoic acid (20:4n-3), to their delta 5 products arachidonic acid (20:4n-6) and eicosapentaenoic acid (20:5n-3), respectively. Therefore, the zebrafish gene encodes a bifunctional enzyme having both delta 5 and delta 6 desaturase activity. This is the first report of a functionally characterized desaturase enzyme of fish, and of a fatty acid desaturase with both delta 5 and delta 6 activity.