Romero D, Brom S, Martínez-Salazar J, Girard M L, Palacios R, Dávila G
Departamento de Genética Molecular, Universidad Nacional Autónoma de México, Cuernavaca, Morelos.
J Bacteriol. 1991 Apr;173(8):2435-41. doi: 10.1128/jb.173.8.2435-2441.1991.
One remarkable characteristic of the genomes of some Rhizobium species is the frequent occurrence of rearrangements. In some instances these rearrangements alter the symbiotic properties of the strains. However, no detailed molecular mechanisms have been proposed for the generation of these rearrangements. To understand the mechanisms involved in the formation of rearrangements in the genome of Rhizobium phaseoli, we have designed a system which allows the positive selection for amplification and deletion events. We have applied this system to investigate the stability of the symbiotic plasmid of R. phaseoli. High-frequency amplification events were detected which increase the copy number of a 120-kb region carrying nodulation and nitrogen fixation genes two to eight times. Deletion events that affect the same region were also found, albeit at a lower frequency. Both kinds of rearrangements are generated by recombination between reiterated nitrogenase (nifHDK) operons flanking the 120-kb region.
某些根瘤菌物种基因组的一个显著特征是重排频繁发生。在某些情况下，这些重排会改变菌株的共生特性。然而，尚未有人提出产生这些重排的详细分子机制。为了了解菜豆根瘤菌基因组重排形成所涉及的机制，我们设计了一个系统，该系统允许对扩增和缺失事件进行正向选择。我们已应用此系统来研究菜豆根瘤菌共生质粒的稳定性。检测到高频扩增事件，该事件使携带结瘤和固氮基因的120 kb区域的拷贝数增加了2至8倍。也发现了影响同一区域的缺失事件，尽管频率较低。这两种重排都是由120 kb区域两侧的重复固氮酶（nifHDK）操纵子之间的重组产生的。
