Plant Molecular Biology Laboratory, Department of Biology, McGill University, Montreal, PQ, Canada H3A 1B1.
Proc Natl Acad Sci U S A. 1985 Jun;82(12):4157-61. doi: 10.1073/pnas.82.12.4157.
A nodulin gene coding for a polypeptide with an apparent M(r) of 24,000 (nodulin-24) was isolated from soybean (Glycine max). DNA sequence analysis of this gene revealed that its coding capacity is for a polypeptide of only M(r) 15,100 and is interrupted by four introns. The three middle exons and their flanking segments appear to have been generated by duplications of a unit resembling an insertion sequence. This unit is bounded by a 12-base-pair inverted repeat and encompasses the 54-base-pair exon corresponding to each of three central hydrophobic domains of the protein, nodulin-24. The resulting repeated hydrophobic structure of this protein may be responsible for an apparent increase in M(r) from 15,100 to 24,000. In vitro translation and immunological studies suggest that nodulin-24 is a precursor and is processed cotranslationally into a M(r) 20,000 polypeptide. This polypeptide is a component of the membrane envelope enclosing the bacteroids (peribacteroid membrane) synthesized during symbiosis with Rhizobium. The low degree (<6%) of sequence divergence among the repeated units suggests that this gene has been generated recently during the evolution of symbiotic nitrogen fixation in soybean.
从大豆（Glycine max）中分离到一个编码具有约 24000Mr 的多肽的豆球蛋白基因。该基因的 DNA 序列分析表明，它的编码能力仅为 Mr15100 的多肽，并被四个内含子所打断。三个中间外显子及其侧翼片段似乎是由类似于插入序列的单元重复产生的。该单元由 12 个碱基对的反向重复序列所限定，并包含与该蛋白的三个中心疏水区相对应的每个 54 个碱基对的外显子，即豆球蛋白-24。该蛋白的重复疏水区结构可能导致 Mr 从 15100 增加到 24000。体外翻译和免疫学研究表明，豆球蛋白-24 是一个前体，并在共翻译过程中被加工成 Mr20000 的多肽。该多肽是与 Rhizobium 共生时合成的类细菌（类周膜）的膜包膜的组成部分。重复单元之间的低序列差异（<6%）表明，该基因是在大豆共生固氮进化过程中最近产生的。
