A omega 3-fatty acid desaturase gene (maw3) which is involved in biosynthesis of n-3 polyunsaturated fatty acids (PUFAs) was previously isolated from Mortierella alpina 1S-4. In this report, we investigated the products of MAW3 catalyzing reaction with endogenous and exogenous fatty acids in the yeast transformant. Two unusual fatty acids de novo synthesized in the yeast transformant expressing maw3 gene were identified as n-4 hexadecadienoic acid (16:2(9cis,12cis)) and n-1 hexadecatrienoic acid (16:3(9cis,12cis,15)) by GC-MS and H-1 NMR analyses. In addition to the desaturation activity at the omega 3-position for 18- and 20-carbon PUFAs, MAW3 in the yeast transformant inserted a double bond at Delta 12-position of endogenous palmitoleic acid (16:1(9cis)) and further at Delta 15-position of the resulting 16:2(9cis,12cis) to result in the formation of 16:3(9cis,12cis,15) leading to a bifunctional Delta 12/Delta 15-desaturase for 16-carbon fatty acids. Moreover, we evaluated the activity of MAW3 in the yeast transformant under different temperatures. The MAW3 did not have desaturation activities in M. alpina 1S-4 at 28 degrees C but it had in the yeast transformant for various fatty acids. The MAW3 was demonstrated to be a trifunctional Delta 12/Delta 15/omega 3-desaturase, exhibiting Delta 12-desaturation for 16:1(9cis), Delta 15-desaturation for 16- and 18-carbon fatty acids that had a preexisting cis-double bond at Delta 12 position, and omega 3-desaturation for 20-carbon fatty acids having that at Delta 14-position. It is the first report that the fatty acid desaturase (MAW3) is shown to have Delta 12- and Delta 15-desaturation activities for a 16-carbon fatty acid, in addition to its major function, omega 3-desaturation activity. (C) 2013, The Society for Biotechnology, Japan. All rights reserved.