Plant Molecular Biology Laboratory, Department of Biology, McGill University, Montreal, Canada.
Proc Natl Acad Sci U S A. 1983 May;80(9):2594-8. doi: 10.1073/pnas.80.9.2594.
Plant gene products that could play a role in the process of symbiotic nitrogen fixation in leguminous plants were detected by screening a cDNA library prepared from soybean nodule poly(A)(+) RNA. About 13% of the 5,700 clones screened contained sequences detectable with a root cDNA probe while about 2,100 clones (37% of the library) contained sequences that were detectable only with nodule cDNA. Five unique sequence species, accounting for more than half of the 2,100 nodule-specific clones, were identified by cross-hybridization experiments. The most abundant species, represented by 860 clones, encodes the well-characterized protein, leghemoglobin (Lb). The other four species, designated NodA, NodB, NodC, and NodD, are represented by 350, 55, 61, and 6 clones, respectively. Each of these four species was found to be encoded by the plant nuclear genome at low copy number. The transcripts corresponding to the nodule-specific clones represented 12-15% (Lb), 6% (NodA), and 0.5-1.1% (NodB, NodC, and NodD) mole fraction of nodule polysomal mRNAs but could not be detected in root polysomal RNA. Hybrid-selection of nodule mRNAs by representative clones and in vitro translation indicated that polypeptides of M(r) 44,000, 27,000, 24,000, and 100,000-120,000 are encoded by NodA, NodB, NodC, and NodD sequences, respectively. These polypeptides reacted with antiserum prepared against total soluble nodule proteins suggesting that the cloned sequences encode nodule-specific proteins, nodulins.
通过筛选从大豆根瘤 poly(A)(+)RNA 制备的 cDNA 文库，检测到可能在豆科植物共生固氮过程中发挥作用的植物基因产物。约 13%的 5700 个克隆含有可被根 cDNA 探针检测到的序列，而约 2100 个克隆（文库的 37%）仅含有可被根瘤 cDNA 检测到的序列。通过杂交实验鉴定了 5 个独特的序列物种，占 2100 个根瘤特异性克隆的一半以上。最丰富的物种由 860 个克隆代表，编码特征良好的蛋白质，即豆血红蛋白（Lb）。其余 4 个物种，分别命名为 NodA、NodB、NodC 和 NodD，分别由 350、55、61 和 6 个克隆代表。这 4 个物种中的每一个都被发现是由植物核基因组以低拷贝数编码的。与根特异克隆相对应的转录物代表了 12-15%（Lb）、6%（NodA）和 0.5-1.1%（NodB、NodC 和 NodD）的豆瘤多核糖体 mRNA 摩尔分数，但在根多核糖体 RNA 中无法检测到。代表克隆对豆瘤 mRNA 的杂交选择和体外翻译表明，M(r)44000、27000、24000 和 100000-120000 的多肽分别由 NodA、NodB、NodC 和 NodD 序列编码。这些多肽与针对总可溶性根瘤蛋白制备的抗血清反应，表明克隆序列编码根瘤特异性蛋白，即结瘤素。
