Krishnan H B, Pueppke S G
Department of Plant Pathology, University of Missouri, Columbia 65211.
Mol Plant Microbe Interact. 1991 Sep-Oct;4(5):521-9. doi: 10.1094/mpmi-4-521.
We have detected strong homology between a 9.2-kb EcoRI restriction fragment from Rhizobium fredii USDA257 that contains nodABC and eight additional EcoRI fragments in DNA digests from this organism. A series of repetitive sequences responsible for this hybridization lies within a 0.95-kb HindIII/SalI subfragment about 1-kb upstream of nodA. This subfragment also hybridizes to multiple restriction fragments from nine other strains of R. fredii, but only one is common to all strains. The 0.95-kb subfragment does not hybridize to genomic DNA from 17 other strains of fast-growing rhizobia, but there is weak homology to two fragments from Rhizobium sp. strain NGR234. We sequenced 2,432 base pairs (bp) of the region encompassing the repetitive sequences. It contains 65 separate 8- to 11-bp inverted and direct repeats, as well as two large open reading frames (ORFs) that overlap on opposite strands. ORF1 reads in the same direction as nodABC, contains 1,071 bp, and encodes a 40.6-kD protein. It has 74% sequence homology to an ORF within the T-DNA of Agrobacterium rhizogenes and similar homology to a series of repetitive sequences from Bradyrhizobium japonicum. ORF2 (981 bp) reads in the opposite direction, encodes a 34.7-kD protein, and has partial identity with a second ORF from A. rhizogenes. We could detect no poly(A)+ nodule transcripts with homology to ORF1 and ORF2. The eight sets of repetitive sequences found in other EcoRI fragments of the genome were cloned from USDA257 on separate cosmids. Some of these cosmids appear to overlap, and two have fragments with homology to nifKDH.
我们在费氏中华根瘤菌USDA257的一个包含nodABC的9.2 kb EcoRI限制性片段与该菌DNA酶切产物中的另外八个EcoRI片段之间检测到了强同源性。一系列导致这种杂交的重复序列位于nodA上游约1 kb处的一个0.95 kb HindIII/SalI亚片段内。该亚片段还与费氏中华根瘤菌其他九个菌株的多个限制性片段杂交，但所有菌株中只有一个片段是共同的。这个0.95 kb的亚片段不与其他17个快速生长根瘤菌菌株的基因组DNA杂交，但与中华根瘤菌NGR234菌株的两个片段有弱同源性。我们对包含重复序列的区域进行了2432个碱基对（bp）的测序。它包含65个单独的8至11 bp的反向和正向重复序列，以及两个在相反链上重叠的大开放阅读框（ORF）。ORF1与nodABC方向相同，包含1071 bp，编码一个40.6 kD的蛋白质。它与发根农杆菌T-DNA内的一个ORF有74%的序列同源性，与日本慢生根瘤菌的一系列重复序列有相似的同源性。ORF2（981 bp）方向相反，编码一个34.7 kD的蛋白质，与发根农杆菌的第二个ORF有部分同一性。我们未检测到与ORF1和ORF2有同源性的聚腺苷酸加尾（poly(A)+）根瘤转录本。基因组其他EcoRI片段中发现的八组重复序列从USDA257分别克隆到了粘粒上。其中一些粘粒似乎有重叠，并且有两个粘粒的片段与nifKDH有同源性。
