CDNA cloning and characterization of human Delta(5)-desaturase involved inthe biosynthesis of arachidonic acid

Two human expressed sequence tag (EST) cDNA sequences with identity with De lta(5)- and Delta(6)-desaturases from a filamentous fungus, Mortierella alp ina, were identified from the LifeSeq(R) database of Incyte Pharmaceuticals , Inc, (Palo Alto, CA, U.S.A.). An oligonucleotide complementary to the 3' EST cDNA sequences was used to screen human liver cDNA using rapid amplific ation of cDNA ends (RACE)-PCR. The amplified DNA fragment had 98% identity with a putative open reading frame (ORF) predicted from a human genomic seq uence, and encoded 444 amino acids. Expression of this ORF in mouse fibrobl ast cells demonstrated that the encoded protein was a Delta(5)-desaturase, as determined by the conversion of dihomo-gamma-linolenic acid (C-20:3,C-n- 6) into arachidonic acid (C-20:4,C-n-6). The human Delta(5)-desaturase cont ained a predicted N-terminal cytochrome b(5)-like domain, as well as three histidine-rich domains. A tissue expression profile revealed that this gene is highly expressed in fetal liver, fetal brain, adult brain and adrenal g land. A search of the existing databases led to localization of this ORF wi thin a 14 kb interval flanked by the flap endonuclease-1 (FEN1) and vitelli form macular dystrophy (Best's disease; VMD2) loci of chromosome 11q12.