The Expression Mechanism of Leghemoglobin Geno of Leguminous Plant.

豆科植物根瘤菌侵染豆科植物后，豆科植物的根瘤中只合成一种小的单体血红素蛋白。lb基因的诱导只发生在细菌感染后，而不依赖于类杆菌中nif基因的表达。根细胞的lb基因表达受侵染细菌的信号诱导。虽然已经对nod-和nif-基因在同源质粒和核苷酸序列上的位点进行了分析，但信号的细节尚不清楚。细胞，豆血红蛋白是在结瘤的最早期阶段合成的，已被间接免疫技术确定。为了分析lb -诱导基因（Lb-ind基因）的表达，我们利用根瘤逆转录酶系统mRNA克隆了lb -基因。用Sau3AI酶切法分离得到三叶草4S总DNA （Nod^+, Lb^+, Fix^+）。将DNA片段与cosmid载体pCKS 13连接，包装在<lambda>-噬菌体头中。将大肠杆菌细胞中的重组DNA通过三亲本配种法转移到三叶草病菌Qn1（Nod^+,Lb^-, Fix^-）上，接种于白三叶草幼苗上。从结核中筛选出菌株NL18（Nod^+, Lb^+, Fix^-）。本研究探讨了三叶草克隆DNA上Lb-ind基因的位置和大小。

Leghemoglobins (Lbs) are small monomeric heme proteins synthesized exclusively in the root nodules that develope due to the rhizobial infection to leguminous plant. The induction of Lb-genes occurs only after bacterial infection but is independent of the expression of nif-gene in bacteroid. The Lb-gene expression of root cells are induced by some signals derived from the invaded bacteria. The signals are not Known about the details although nod- and nif-gene have been analyzed about the loci on Sym-plasmid and nucleotide sequences.The cell, leghemoglobin is synthesized at the most early step of nodulation, has been determined by an indirect-immunological technique.For analysis the expression of Lb-induction gene(Lb-ind gene), Lb-gene has been cloned with the mRNA of root nodule : reverse transcriptase system. The total DNA from R. trifolii 4S(Nod^+, Lb^+, Fix^+) was isolated and digested with Sau3AI. The DNA fragments were ligated with cosmid vector pCKS 13 and packaged in <lambda>-phage head. The recombinant DNA including in E. coli cells were transferred to R. trifolii Qn1(Nod^+,Lb^-, Fix^-) by triparental mating method, and then inoculated to seedilings of white clover. A strain NL18(Nod^+, Lb^+, Fix^-) was screened out form a nodule. The locus and size of Lb-ind gene on the cloning DNA from R. trifolii 4S was discussed in this study.