Molecular cloning and functional characterization of rat delta-6 fatty acid desaturase

Mammalian cDNA fragments putatively encoding amino acid sequences characteristic of the fatty acid desaturase were obtained using expressed sequence tag (EST) sequence informations. These fragments were subsequently used to screen a rat liver cDNA library, yielding a 1573-bp clone. Expression of DNA fragment containing either of two possible open reading frames (nucleotide numbers 97-1431 and 148-1431) of the isolated clone in yeast led to the accumulation of gamma-linolenic acid in the presence of exogenous linoleic acid. In this system, the addition of alpha-linolenic acid also resulted in the accumulation of its Delta-6 desaturated product whereas dihomo-gamma-linolenic acid failed to be a substrate. These results indicate that the protein encoded by the rat cDNA is Delta-6 fatty acid desaturase, and the first 17 amino acids corresponding to the coding region 97-147 of the clone are not required to function in yeast.