Fig. 1. fat-3 encodes a 6-desaturase. (A) The LC-PUFA synthetic pathways (Lauritzen et al., 2001; Spychalla et al., 1997). ALA, -linolenic acid; LIN, linoleic acid; DGLA, dihomo--linolenic acid; EPA, eicosapentaenoic acid; AA, arachidonic acid; DHA, docosahexaenoic acid. (B) The fat-3 gene (W08D2.4) is located on chromosome IV, between unc-24 and dpy-20. A 4.7 kb genomic fragment including 977 bp 5' and 862 bp 3' of the fat-3 coding region rescues fat-3 mutants. The coding regions are in boxes and the non-coding regions are shown as lines. The cytochrome b₅-like domain is in gray. Asterisks indicate histidine-rich regions. The fat-3(lg8101) and fat-3(qa1811) deletions and their breakpoints are shown. T indicates an A to T substitution. Dp indicates a 17 bp duplication (GAAAATGGTTGAATCAT). fat-3(wa22) is a C to T point mutation that changes S₁₈₆ to F. (C) ClustalX alignment of FAT-3 protein with human and plant (Borago officinalis) 6-desaturases. The triangle indicates the fat-3(wa22) mutation. Single-letter abbreviations for amino acid residues are used. Identical and similar amino acids are identified by gray and light gray shading, respectively. The putative cytochrome b₅-like domain is indicated with a line. Histidines important for catalytic activity are marked by asterisks.