CLONING OF OMEGA-3 DESATURASE FROM CYANOBACTERIA AND ITS USE IN ALTERING THE DEGREE OF MEMBRANE-LIPID UNSATURATION

Cyanobacteria respond to a decrease in temperature by desaturating fat ty acids of membrane lipids to compensate for the decrease in membrane fluidity. Among various desaturation reactions in cyanobacteria, the desaturation of the omega 3 position of fatty acids is the most sensit ive to the change in temperature. In the present study, we isolated a gene, designated desB, for the omega 3 desaturase from the cyanobacter ium, Synechocystis sp. PCC 6803. The desB gene encodes a protein a 359 amino-acid residues with molecular mass of 41.9 kDa. The desB gene is transcribed as a monocistronic operon that produced a single transcri pt of 1.4 kb. The level of the desB transcript in cells grown at 22 de grees C was 10 times higher than that in cells grown at 34 degrees C. In order to manipulate the fatty-acid unsaturation of membrane lipids, the desB gene in Synechocystis sp. PCC 6803 was mutated by insertion of a kanamycin-resistance gene cartridge. The resultant mutant was una ble to desaturate fatty acids at the omega 3 position. The desA gene, which encodes the Delta 12 desaturase of Synechocystis sp. PCC 6803, a nd the desB gene were introduced into Synechococcus sp. PCC 7942. Whil st the parent cyanobacterium can only desaturate membrane lipids at th e Delta 9 position of fatty acids, the resultant transformant was able to desaturate fatty acids of membrane lipids at the Delta 9, Delta 12 and omega 3 positions. These results confirm the function of the desB gene and demonstrate that it is possible to genetically manipulate th e fatty-acid unsaturation of membrane lipids in cyanobacteria.