Piper K R, Beck von Bodman S, Farrand S K
Department of Plant Pathology, University of Illinois, Urbana/Champaign 61801.
Nature. 1993 Apr 1;362(6419):448-50. doi: 10.1038/362448a0.
Conjugal transfer of Ti plasmids from Agrobacterium donors to bacterial recipients is controlled by two types of diffusible signal molecules. Induction is mediated by novel compounds, called opines, that are secreted by crown gall tumours. These neoplasias result from infection of susceptible plants by virulent agrobacteria. The second diffusible signal, called conjugation factor, is synthesized by the donor bacteria themselves. Production of this factor is induced by the opine. Here we show that conjugation is regulated directly by a transcriptional activator, TraR, which requires conjugation factor as a coinducer to activate tra gene expression. TraR is a homologue of LuxR, the lux gene activator from Vibrio fischeri which also requires an endogenously synthesized diffusible coinducer. The two regulatory systems are related; the two activator proteins show amino-acid sequence similarities and the lux system cofactor, autoinducer, will substitute for conjugation factor in the TraR-dependent activation of Ti plasmid tra genes.
Ti质粒从农杆菌供体向细菌受体的接合转移受两种可扩散信号分子的控制。诱导作用由冠瘿瘤分泌的一类名为冠瘿碱的新化合物介导。这些肿瘤形成是由毒性农杆菌感染易感植物所致。第二种可扩散信号称为接合因子，由供体细菌自身合成。该因子的产生由冠瘿碱诱导。我们在此表明，接合作用直接受转录激活因子TraR调控，TraR需要接合因子作为共诱导剂来激活tra基因表达。TraR是费氏弧菌lux基因激活因子LuxR的同源物，LuxR也需要内源性合成的可扩散共诱导剂。这两种调控系统相关；两种激活蛋白显示出氨基酸序列相似性，并且lux系统的辅因子自体诱导物在TraR依赖的Ti质粒tra基因激活中可替代接合因子。
