Perret X, Broughton W J, Brenner S
Laboratoire de Biologie Moléculaire des Plantes Supérieures, Université de Genève, Switzerland.
Proc Natl Acad Sci U S A. 1991 Mar 1;88(5):1923-7. doi: 10.1073/pnas.88.5.1923.
Many of the bacterial genes involved in nodulation (nod) and nitrogen fixation (nif) are dispersed over the 500-kilobase plasmid pNGR234a of the broad host-range Rhizobium species NGR234. As a first step toward generating a complete physical and genetic map of the plasmid, a full overlapping collection of cosmids was derived from a total genomic library. Clones were aligned by combining fingerprinting, hybridization, and pulsed-field gel electrophoresis data. Symbiotic loci were localized by probing a representative set of cosmids with both homologous and heterologous genes. nodABC, nodD1, nodD2, nodSU, nolB, and region II are widely dispersed over pNGR234a, while the two functional copies of nifKDH are separated by only 28 kilobases. Interestingly, sequences homologous to nodE, nodG, nodP, and nodQ have been assigned to another autonomously replicating element in Rhizobium species NGR234. Similarly one copy of the structural dctA gene is located on the symbiotic plasmid (dctA1) while the other is on what we assume to be the chromosome.
许多参与根瘤形成（nod）和固氮（nif）的细菌基因分散在广宿主范围的根瘤菌NGR234的500千碱基质粒pNGR234a上。作为构建该质粒完整物理图谱和遗传图谱的第一步，从一个全基因组文库中获得了一个完整的重叠黏粒文库。通过整合指纹图谱、杂交和脉冲场凝胶电泳数据来比对克隆。通过用同源和异源基因探测一组代表性的黏粒来定位共生基因座。nodABC、nodD1、nodD2、nodSU、nolB和区域II广泛分散在pNGR234a上，而nifKDH的两个功能拷贝仅相隔28千碱基。有趣的是，与nodE、nodG、nodP和nodQ同源的序列已被定位到根瘤菌NGR234中的另一个自主复制元件上。同样，结构dctA基因的一个拷贝位于共生质粒上（dctA1），而另一个位于我们认为是染色体的位置上。
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