Sakamoto T, Los D A, Higashi S, Wada H, Nishida I, Ohmori M, Murata N
Department of Molecular Biomechanics, Graduate University of Advanced Studies, Okazaki, Japan.
Plant Mol Biol. 1994 Oct;26(1):249-63. doi: 10.1007/BF00039536.
Cyanobacteria respond to a decrease in temperature by desaturating fatty 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 sensitive to the change in temperature. In the present study, we isolated a gene, designated desB, for the omega 3 desaturase from the cyanobacterium, 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 transcript of 1.4 kb. The level of the desB transcript in cells grown at 22 degrees 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 unable to desaturate fatty acids at the omega 3 position. The desA gene, which encodes the delta 12 desaturase of Synechocystis sp. PCC 6803, and the desB gene were introduced into Synechococcus sp. PCC 7942. Whilst the parent cyanobacterium can only desaturate membrane lipids at the 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 the fatty-acid unsaturation of membrane lipids in cyanobacteria.
蓝细菌通过使膜脂脂肪酸去饱和来应对温度降低，以补偿膜流动性的下降。在蓝细菌的各种去饱和反应中，脂肪酸ω-3位的去饱和对温度变化最为敏感。在本研究中，我们从蓝细菌集胞藻PCC 6803中分离出一个编码ω-3去饱和酶的基因，命名为desB。desB基因编码一个由359个氨基酸残基组成、分子量为41.9 kDa的蛋白质。desB基因作为一个单顺反子操纵子进行转录，产生一个1.4 kb的单一转录本。在22℃生长的细胞中desB转录本的水平比在34℃生长的细胞中高10倍。为了操纵膜脂的脂肪酸不饱和度，通过插入卡那霉素抗性基因盒对集胞藻PCC 6803中的desB基因进行突变。所得突变体无法使脂肪酸在ω-3位去饱和。将编码集胞藻PCC 6803的δ-12去饱和酶的desA基因和desB基因导入聚球藻PCC 7942。亲本蓝细菌只能使脂肪酸在δ-9位去饱和，而所得转化体能够使膜脂脂肪酸在δ-9、δ-12和ω-3位去饱和。这些结果证实了desB基因的功能，并表明可以对蓝细菌中膜脂的脂肪酸不饱和度进行基因操作。
