DELTA-9 FATTY-ACID DESATURASE GENE CONTAINING A CARBOXYL-TERMINAL CYTOCHROME B5 DOMAIN FROM THE RED ALGA CYANIDIOSCHYZON MEROLAE

A delta-9 fatty acid desaturase gene, homologous to animal and fungal acyl-coenzyme A (CoA) desaturases, was isolated from the red alga Cyan idioschyzon merolae using a degenerate PCR strategy. This gene, design ated as CmFAD9, has no intron. The encoded delta-9 fatty acid desatura se (CmFad9p) consists of 476 amino acids and has an estimated molecula r mass of 55.4 kDa. CmFad9p is a unique delta-9 fatty acid desaturase among plants, in that it is fused with the cytochrome b5 domain at its carboxyl terminus. This is characteristic of yeast acyl-CoA desaturas e. Genomic Southern hybridization suggested that the C. merolae genome contains a single gene for delta-9 fatty acid desaturase of the anima l and fungal type. Southern hybridization combined with pulsed-field g el electrophoresis revealed that CmFAD9 is probably located on chromos ome XI of the 17 C. merolae chromosomes. A 1.6-kb product of this gene was transcribed throughout a light/dark synchronization culture. The discovery of CmFAD9 indicates the existence of a novel type of plant d elta-9 fatty acid desaturase that may function in the endoplasmic reti culum, but not in the plastid.