植物细胞的细胞壁主要由纤维素、半纤维素和木质素等物质组成。木聚糖是植物半纤维素的重要组分，是自然界中除纤维素外最为丰富的多糖，也是自然界中主要的可再生资源。由于木聚糖结构复杂，它的完全降解需要木聚糖水解酶系中各种酶相互之间协同完成，其中β-1, 4-木聚糖酶（简称木聚糖酶，EC 3.2.1.8）是最关键的水解酶。木聚糖酶的应用极其广泛，可用于造纸、食品、饲料添加剂、生物转化、能源、纺织等方面，尤其是当前迫切的环境问题将进一步促使木聚糖酶研究的开展。 本研究以浅青紫链霉菌（Streptomyces lividans）β-1, 4-木聚糖酶（简称木聚糖酶）为研究对象，把木聚糖酶基因xynB在大肠杆菌中进行克隆表达并对其表达产物进行了酶学性质的研究。本论文主要进行了以下几个方面的研究工作：1. 木聚糖酶基因xynB的克隆、测序；2. xynB基因表达载体的构建；3. xynB基因在大肠杆菌中的诱导表达；4. 重组木聚糖酶酶学性质研究。 本论文主要研究结果如下：1. 以浅青紫链霉菌（Streptomyces lividans）基因组DNA为模板，利用自行设计的引物1和引物2，进行常规的PCR扩增反应，成功地克隆出木聚糖酶基因xynB。基因测序结果与文献报道的完全一致，浅青紫链霉菌木聚糖酶XYNB属于G/11族。2. PCR扩增的木聚糖酶基因（xynB）通过BamHI和Xho I位点，与大肠杆菌表达载体pET-21a上的多克隆位点融合，构建成重组表达载体pET-21a—SLB。用该重组表达质粒转化大肠杆菌BL21，获得重组工程菌。经30oC IPTG诱导4 hrs，重组木聚糖酶活力可达168.1 IU/ml培养物。3. 重组木聚糖酶的分子量约为33 kDa，与理论推算的分子量（31.1 kDa）相吻合。该酶的最适作用温度为50oC；该酶在最适温度时相对比较稳定；木聚糖酶的最适作用pH值为6.2；稳定pH范围在pH 5.0~10.0之间，碱稳定性较强，适合用于制浆造纸工业。

Plant cell walls contain three major polymers: cellulose, hemicellulose and lignin. Xylan is the major hemicellulose in plants. Second to cellulose, xylan is the most abundant renewable polysaccharides in nature. Because xylan is complex in structure, its biodegradation involves the actions of several xylanolytic enzymes, of which the β-1, 4-xylanase (for short: xylanase, EC 3.2.1.8) is the most important one. The application of xylanase is extremely extensive. Xylanase can be widely used in paper, food, fodder, bio-transformation, energy, textile and many other industries. The study of the xylanase will be enhanced especially in nowadays urgent environmental issues. The research object of this study is β-1,4-xylanase from Streptomyces lividans. The xylanase gene was cloned and expressed in E. coli and in the same time the properties of the recombinant xylanase were analyzed in this study. This thesis contains following four parts:1. Cloning and sequencing of xynB gene;2. Construction of Streptomyces lividans expression vector;3. Expression of xynB gene in E. coli;4. Studies on properties of the recombinant xylanase. The detailed results and conclusions were as follows:1. The gene fragment encoding S.lividans xylanase (xynB) was cloned successfully from S. lividans genome DNA by PCR method using Primer1 and Primer2. Sequence analysis showed that the xynB gene cloned was identical with the gene reported.2. The recombinant expression vector pET-21a—SLB was constructed by ligating the xynB gene cloned by PCR and on pET-21a with T4 DNA ligase in BamHI and Xho I sites. This expression vector pET-21a—SLB transformed E. coli BL21, which can obtain recombinant strain. Induced by IPTG at 30oC, the xynB gene was expressed in E. coli BL21, and the recombinant xylanase activity reached to 168.1 IU/ml.3. The molecular mass of the recombinant xylanase was about 33 kDa, this was almost the same as the molecular mass of the xylanase calculated from the deduced amino acid sequence (31.1 kDa). Optimum reaction temperature of the xylanase was 50oC, and it was relatively stable on this optimum temperature. Optimum pH was 6.2, and xylanase showed to have a good activity over a broad pH range from 5.0 to 10.0, quite suitable to use in paper and pulp making industry.