Delta-12 desaturases are involved in the conversion of oleic acid to linoleic acid in plant. Based on the conserved oligo amino acid residues of the published delta-12 desaturase genes from other higher plant species,a cDNA fragment was amplified by RT-PCR (reverse transcriptase-polymerase chain reaction) from the total RNA of immature maize embryos. According to bioinformation analysis of the cDNA sequence, a specific fragment of FAD2 gene was isolated by RT-PCR from immature maize embryos, and DNA of the same length was amplified from maize genome. Results of sequence analysis indicate that they are all 1 164 bp long,and have just an open reading frame (ORF) coding for 387 amino acids, and there is no intron in the FAD2 ORF(GenBank accession DQ496227). The deduced amino acid sequence of the cloned FAD2 showed high identity to those of other plant delta-12 fatty acid desaturases. It contains three histidine motifs and two long stretches of hydrophobic residues, indicative of an integral membrane protein spanning membrane four times. Analysis by semiquantitive RT-PCR showed that FAD2 was strongly expressed in maize immature embryos than in leaves, stems and roots.%高等植物中的△12脂肪酸脱饱和酶是将油酸转化为亚油酸的酶.根据已发表的其他高等植物的FAD2基因的保守序列设计同源引物,通过RT-PCR从玉米幼胚中扩增得到一个特异的cDNA基因片段.通过生物信息学分析,从玉米幼胚cDNA和基因组中均扩增得到1 164 bp FAD2基因(GenBank登陆号:DQ496227),它编码387个氨基酸,含有完整的ORF框,在ORF框内无内含子.序列联配与树状分析结果表明,FAD2推导的氨基酸序列与其他物种的△12脱饱和酶基因具有同源性.它含有3个组氨酸保守域和2段很长的疏水区,是一个跨膜4次的膜结合蛋白.半定量RT-PCR分析显示FAD2基因在玉米幼胚中表达量最高,在叶、茎、根中亦有低水平表达.
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