Close T J, Tait R C, Kado C I
J Bacteriol. 1985 Nov;164(2):774-81. doi: 10.1128/jb.164.2.774-781.1985.
We isolated a mutant strain of Agrobacterium tumefaciens, designated Ros, that has a pleiotropic phenotype which includes elevated levels of expression of certain genes in the virulence (Vir) region of tumor-inducing plasmid pTiC58. This mutant and others were isolated by fusing the promoter of the Vir bak gene to a promoterless gene (cat) that encodes chloramphenicol acetyltransferase and then selecting for increased expression of cat in A. tumefaciens. The ros mutation is chromosomal in nature and is characterized by a more-than-300-fold increase in the level of expression of bak and a 12-fold increase in the level of expression of an adjacent divergent operon containing the hdv genes, which are involved in some aspect of host specificity. The Ros mutant is fully virulent and is typified by its unusual colony morphology; the colonies have rough surfaces, uneven edges, and a pit in the center at 24 degrees C and vary markedly in appearance from one growth temperature to another. The Ros mutant is not able to form colonies at 12 degrees C, a temperature at which the wild-type strain forms colonies in 14 days. The ros mutation occurs spontaneously with a frequency of 5 X 10(-8). Genetic and biochemical evidence indicates that the product of the ros locus is a negative regulator of Ti plasmid genes and is related to undefined chromosomally encoded functions that are involved in the mutant phenotype.
我们分离出了一种根癌土壤杆菌的突变菌株，命名为Ros，它具有多效性表型，包括肿瘤诱导质粒pTiC58毒力（Vir）区域中某些基因的表达水平升高。通过将Vir bak基因的启动子与编码氯霉素乙酰转移酶的无启动子基因（cat）融合，然后在根癌土壤杆菌中选择cat表达增加的菌株，分离出了这种突变体和其他突变体。ros突变本质上是染色体突变，其特征是bak的表达水平增加了300多倍，以及一个包含hdv基因的相邻反向操纵子的表达水平增加了12倍，hdv基因与宿主特异性的某些方面有关。Ros突变体具有完全的毒性，其典型特征是异常的菌落形态；在24℃时，菌落表面粗糙、边缘不平整且中心有一个凹坑，并且在不同生长温度下外观差异明显。Ros突变体在12℃时无法形成菌落，而野生型菌株在该温度下14天内可形成菌落。ros突变自发发生的频率为5×10^(-8)。遗传和生化证据表明，ros位点的产物是Ti质粒基因的负调控因子，并且与参与突变体表型的未定义染色体编码功能有关。
