玉米waxy基因的密码子用法特征的分析.doc

玉米waxy基因的密码子用法特征分析 生物科学 2003 级 顾 勇 指导教师： 刘汉梅 助 教（硕士） 摘要：密码子简并性特征造成了不同物种密码子使用的偏好性不同，这对外源基因的表达强度有着较大的影响。本研究应用EMB0SS的CUSP、CHIPS程序和CodonW软件对玉米waxy基因的密码子进行了分析，并将分析结果分别与6种植物的waxy基因和大肠杆菌、酵母基因组的密码子偏爱性进行比较。结果表明：（1）玉米、水稻等5种禾本科单子叶植物的waxy基因密码子用法特征相似，偏向于使用以G或C结尾的密码子，而双子叶植物拟南芥、豌豆的waxy基因密码子偏好性则相反，它们偏向于使用以A或T结尾的密码子。（2）玉米waxy基因与大肠杆菌、酵母的密码子偏爱性有较大差异,分析结果对玉米waxy基因在这两类表达系统中的表达具有一定指导意义。 关键词：同义密码子偏性；玉米；waxy基因 The Features of Synonymous Codon Bias in Zea mays Biological Science Grade 2003 Gu Yong Directed by Liu Han-Mei (assistant) Abstract: The difference of codon usage bias in different species was caused by codon　preference, which affected foreign gene expression. Waxy gene sequences of Zea mays were analyzed with cusp program of EMBOSS and CodonW program. A comparison of synonymous codon usage bias of Waxy gene was made between maize and seven species as well as maize and E.coli genome or yeast genome．Results show that waxy gene of Monocotyledoneae Gramineae Poaceae had a specific codon usage bias, which differed from that of Dicotyledoneae Gramineae Poaceae. The codons, which were biased most, like those in Monocotyledoneae Gramineae Poaceae were mainly G-ending or C-ending codons other than A-ending or T-ending codons in Dicotyledoneae Gramineae Poaceae. Codon usage bias of waxy gene in Zea mays was greatly different from that of E.coli genome and yeast genome. The result would benefit the research on waxy gene expression in two kinds of expression system. Key words：odon usage bias, Zea mays, waxy gene 淀粉是禾谷类作物胚乳的主要贮藏物质，按结构可将其分为直链淀粉和支链淀粉。直链淀粉是在颗粒结合型淀粉合成酶（Granule-bound starch synthase,GBSS）a-1，4-糖苷键进行葡聚糖链的延伸，当链达到一定长度后，在淀粉分支酶（Starch branching enzyme，SBE）作用下，在线性糖链内部引入a-1,6-糖苷键形成分支，并进一步在SSS催化下延长分支，最后淀粉去分支酶（DBE）对分支进行修饰，最终合成具有一定结构特性的淀粉结晶体[1，2]GBSS有两个同工酶，分别是GBSSⅠ和GBSS Ⅱ， GBSSⅠ由位于9号染色体短臂的waxy基因编码，主要控制玉米胚乳和花粉的直链淀粉合成，而GBSS Ⅱ主要控制叶片的直链淀粉合成。如果waxy基因缺失、表达受阻或GBSSⅠ酶活性降低，将导致直链淀粉合成受阻，含量较低，从而改变淀粉的糊化和膨胀特性。研究表明糯玉米具有许多优良特性，其籽粒胚乳中的淀粉几乎全为支链淀粉，而它的糯质表现型就是受隐性突变的waxy基因控制。 编码同一氨基酸的密