摘要
通过原位杂交从巴西固氮螺菌Yu62的基因文库中 ,筛选到glnB基因的阳性克隆 ,将3 7kb/EcoRI+PstI的阳性克隆亚克隆到pUC1 9中 ,进行了全序列分析 ,其在GenBank中的登记号是AF32 3960。DNA序列分析表明该阳性克隆含有完整的glnB基因 ,glnB基因下游是编码谷氨酰胺合成酶 (GS)的glnA基因 ,glnB基因上游是一个编码未知蛋白的ORF。glnB基因编码区长 336bp,编码 1 1 2个氨基酸 ,与肺炎克氏杆菌、大豆慢生根瘤菌、豌豆根瘤菌及大肠杆菌在氨基酸顺序的同源性分别高达 71 %、77%、79%和 69%。将卡那霉素抗性片段 (Km -cas sette)插入glnB基因的BglII位点 ,通过三亲杂交法将其引入到巴西固氮螺菌Yu62中 ,通过同源重组 ,获得GlnB- 突变株 (glnB ::Km)。为了进一步分析glnB基因的功能 ,将glnB基因的编码区 ( 339bp)构建在pVK1 0 0中 ,置于Km启动子下组成型表达 ,形成重组质粒pVK -II。将重组质粒pVK -II转入到GlnB- 突变株 ,构建成互补株C -glnB(glnB ::Km/glnB)。对GlnB-突变株和互补株的固氮酶活性和生长性能的测定表明 ,GlnB- 突变体无固氮酶活性 ,即表型为Nif- ;而互补株像野生型菌株一样具有固氮酶活性。突变株、互补株及野生型在菌落生长速度上基本相同。将含有glnB基因的重组质粒pVK -II分别转移到野生型Yu62?
The glnB gene of A. brasilense Yu62 was determined in a 3.7kb Eco RI+ Pst I fragment. The glnA is located downstream of glnB and an ORF for hypothetical protein is on upstream of glnB . The deduced amino acid sequence of P II encoded by glnB is 71%, 77%, 79% and 69% identical to that of K. pneumoniae, Bradyrhizobium japonicum, Rhizobium leguminosarum and E. coli, respectively. A Km-cassette was inserted into Bgl II site of glnB coding region and GlnB - mutant was obtained by homologous recombination. The GlnB - mutant has lost the nitrogenase activity, ie: Nif -. For the functional confirmation of glnB gene, a complementary test was carried out and it was shown that C-glnB(glnB::Km/glnB ) can restore the nitrogenase activity. When the recombinant plasmid pVK-II which containined the coding region of glnB was introduced into A. brasilense Yu62 and A. brasilense Yu62 DraT -, respectively, the Yu62-II (containing pVK-II) and draT-II(containing pVK-II) showed higher nitrogenase activity than wild type. These results confirmed that glnB plays an important role in the regulation of nitrogen in A. brasilense.
基金
国家 8 63高科技计划 ( 863-1 0 1 -0 3-0 4 -0 2 )
国家自然科学基金 ( 30 0 70 4 0 7)资助项目~~
