A second functional Delta 5 fatty acid desaturase in the cellular slime mould Dictyostelium discoideum

A cDNA with homology to fatty acid desaturases was selected by searching th e cDNA data bank of Dictyostelium discoideum (http://www.csm.biol.tsukuba.a c.jp/cDNAproject.html) with conserved histidine box motifs. Using this sequ ence, genomic DNA encoding the Delta 5 desaturase was amplified from the ge nomic DNA of D. discoideum, and its desaturase activity was confirmed by th e overexpression mutation in D. discoideum and the gain-of-function mutatio n in yeast. The cloned cDNA is 1565 nucleotides in length, and the deduced amino-acid sequence comprised 467 amino-acid residues containing an N-termi nal cytochrome b5 domain that shared 43% identity with cytochrome b5 of Ory za sativa. The whole sequence was 42% identical to the Delta 5 desaturase o f Mortierella alpina. This desaturase is a novel member of the cytochrome b 5-containing Delta 5 fatty acid desaturase. As we have already reported one other Delta 5 desaturase in Dictyostelium, this organism is the first to b e confirmed as having two functional Delta 5 fatty acid desaturase genes. T he substrate specificities of the two functional Delta 5 desaturases of D. discoideum were also examined.