中文摘要：

多聚半乳糖醛酸酶（polygalacturonase,PG）广泛存在于细菌、真菌和植物中,目前数据库中已积累了大量的序列资料。为了进一步了解PG基因家族的分子进化,以及其作为系统进化研究材料的可能性,本研究选取了88条来自不同物种包括细菌、真菌和植物的PG蛋白序列,用CLUSTALW程序对其氨基酸序列进行了联配,并用邻位相接法构建了系统进化树。结果表明,尽管不同来源的PG序列表现了很大的差异,但仍有4个保守性极强的结构域存在（175NTD、197DD、218GHG和250RIK）;同时发现在PG序列中大多数的Cys位点均具有较好的保守性,而且在细菌、真菌和植物的PG序列中各有自身保守的Cys位点,Cys的保守性体现了物种的分类关系;进一步构建分子进化树显示,PG基因基本上首先根据物种类型而聚类,明显地划分为细菌、真菌和植物三大类;其次,不同作用方式的内切PG（endo-PG）和外切PG（exo-PG）在各类群中也都处于完全独立的分支中。

英文摘要：

Polygalacturonase（PG） is widely distributed in bacteria,fungi and plants,and a number of PG sequences are now in the searchable databases.To further study the molecular evolution patterns of PGs and the feasibility of species phylogeny using PG gene,in this research,eghty-eight PG sequences of bacteria,fungi and plants were collected from GenBank,EMBL and DDBJ database.All sequence alignments were performed using the program Clustal W.The evolutionary tree was constructed by neighboring-joining（N-J） method.The amino acid sequence alignment of all PG sequences confirmed that there were four strictly conserved sequence domains（175NTD,197DD,218GHG and 250RIK）.And some conserved cysteine sites were also found,and the corresponding sites could be conserved only in the respective frames of the bacterial,fungal and plant groups,which could reflect classification of organisms.The constructed evolutionary tree manifested that basically there were three main group：bacteria,fungi and plants.Furthermore,the endo-and exo-mode of action of PGs in the respective frames of the bacterial,fungal and plant groups also formed independent clade.