玉米△12脂肪酸脱氢酶基因（FAD2）在酿酒酵母中的表达

玉米△12脂肪酸脱氢酶是催化油酸形成亚油酸的关键酶。将其编码基因FAD2（GenBank登陆号：DQ496227）克隆到酿酒酵母表达载体pYES2．0中，构建成重组质粒pYE／FAD2，转化到酿酒酵母进行诱导表达，同时以pYES2．0转化子为对照。气相色谱（Gc）分析表明，重组转化子亚油酸的含量占酵母总脂肪酸的1．54％，而对照未检测到亚油酸。表明FAD2基因具有编码△12脂肪酸脱氢酶的功能。为探索转译起始密码子周边序列的改变对FAD2基因表达产生的影响，将该基因的起始密码子上游序列进行修改，构建重组表达载体pYE／FAD2—1，转化酿酒酵母进行表达。GC分析表明，pYE／FAD2—1转化子的亚油酸含量占总脂肪酸含量的8．81％，是对照pYE／FAD2转化子的近5倍。

Functional Expression of a Delta-12 Fatty Acid Desaturase Gene (FAD2) from Zea mays in Saccharomyces cerevisiae

Delta-12 fatty acid desaturase is the key enzyme converting oleic acid to linoleic acid in maize. To identify the function of delta-12 fatty acid desaturase gene （FAD2, GenBank accession No. DQ496227） from Zea mays, the open reading frame of the gene was subcloned into expression vector pYES2.0. A recombinant plasmid pYE/FAD2 was constructed and then transformed into Saccharomyces cerevisiae, along with the yeasts transformed with shuttle vector pYES2.0 as controls. Gas chromatogram （GC） analysis of the resultant fatty acid methyl esters showed that the transformed yeast cells expressing FAD2 had a linoleic acid content of 1.54 % of total fatty acid content, not present in control yeast cells, indicating that the gene encodes a functional delta-12 fatty acid desaturase. Further, with modification of sequences flanking AUG codon of the FAD2 gene, a recombinant plasmid pYE/FAD2-1was constructed and transformed into S. c for expression. As a result, the percentage of linoleic acid to total fatty acids in FAD2-1 transformed yeasts was 8.81%, about five fold of the control. The results demonstrated that the modification of sequences flanking AUG codon will facilitate the expression level of the delta-12-fatty acid desaturase gene.