中文摘要：

从南方红豆杉Taxuswallichianavar．mairei的新鲜嫩叶中提取基因组DNA作为模板，利用三组特异引物进行PCR扩增，然后克隆测序得到紫杉烷7β-羟基化酶的基因全长。该基因编码区起始密码子为ATG，终止密码子为TGA，全长1692bp；碱基组成为490A（29．0％），351C（20．7％），362G（21．4％）和489T（28．9％）。将紫杉烷7β-羟基化酶基因全长序列与细胞色素P450基因家族的其它三个成员进行比对，发现它与紫杉烷2α-羟基化酶基因、紫杉烷10β-羟基化酶基因及紫杉烷13α-羟基化酶基因的一致性分别为74％、68％及76％。它们的外显子和内含子的连接区均具保守的GT—AG结构，内含子区的变异性明显高于外显子区。进一步以红豆杉属的13个紫杉烷羟基化酶基因家族成员为对象，利用位点间可变ω（非同义替换率dN和同义替换率dS的比值）模型对该基因家族的适应性进化进行分析。分支模型、位点模型以及分支一位点模型的分析表明：紫杉烷羟基化酶基因家族的少数分支处于正选择压力下（ω〉1），但未检测到正选择位点；而绝大部分位点受强烈的负选择作用（ω〈1）。

英文摘要：

By using PCR and cloning approches, a full-length sequence （ 1 692 bp） of taxoid 7β- hydroxylase gene was obtained from Taxus wallichiarta var. mairei genomie DNA. The gene sequence contains 490 adenine （29.0%） , 351 cytosine （20. 7% ） , 362 guanine （21.4%） and 489 thymine （28.9%） , using ATG and TGA as start and stop codons. Senquence comparisons reveal that the T. wallichiana vat. mairei taxoid 7β-hydroxylase gene is highly similar to other P450 gene family members. It shows a identity of 74% with taxoid 2α-hydroxylase, 68% with taxoid 10β-hydroxylase, and 76% with taxoid 13α-hydroxylase. The joint region between introns and extons possess the conserved GT-AG, and introns exhibit higher variability than extrons. An evolutionary analysis was further performed on the P450 gene family members under models allowing ω （nonsynonymous/synonymsous rate ratio） to vary among sites. Under the branch model, the site model and the branch-site model developed by Yang et al, the results show that although several lineages are under positive selection withω 〉 1, no positively se-lected sites are identified; and most of the sites in this gene family are under negative selection with ω〈 1.