Toman Z, Dambly-Chaudière C, Tenenbaum L, Radman M
J Mol Biol. 1985 Nov 5;186(1):97-105. doi: 10.1016/0022-2836(85)90260-8.
In order to compare the genetic and epigenetic effects of genotoxic agents, we have constructed Escherichia coli K12 strains that allow the detection of mutagenesis, SOS induction (epigenetic effect) and genetic recombination in the same genetic background. The epigenetic effect was detected in a similar way to any genetic alteration, i.e. by counting altered clones (colonies), using a gene fusion system that responds to a temporary epigenetic effect by a stable, heritable switch. The gene fusion consists of the E. coli gal operon and a partially deleted prophage lambda, resulting in the gal operon coming under the control of the cI and cro genes. It allows the detection of SOS induction and forward mutagenesis in the cI gene. Even a temporary inactivation of the CI repressor in this particular system leads to a stable epigenetic switch transmitted to the cellular progeny, which can be detected as Gal+ (red) colonies. The genetic (mutational inactivation of gene cI) and epigenetic (proteolytic inactivation of the product of gene cI) mechanisms leading to gal expression can be distinguished. Genetic recombination between two heteroallelic lacZ genes, one located in the bacterial chromosome, the other on an F'lac plasmid, can be detected as Lac+ colonies. Radiation and several chemical mutagens show very different capacities in generating mutants, inductants and recombinants; therefore, a dose range of any physical or chemical agent generates a set of relative values for the generation of mutants, inductants and recombinants that are characteristic of the agent.
为了比较遗传毒性剂的遗传和表观遗传效应，我们构建了大肠杆菌K12菌株，该菌株能够在相同遗传背景下检测诱变、SOS诱导（表观遗传效应）和遗传重组。表观遗传效应的检测方式与任何遗传改变类似，即通过计数改变的克隆（菌落），使用一种基因融合系统，该系统通过稳定的、可遗传的开关对暂时的表观遗传效应做出反应。基因融合由大肠杆菌gal操纵子和部分缺失的λ原噬菌体组成，导致gal操纵子受cI和cro基因的控制。它能够检测cI基因中的SOS诱导和正向诱变。在这个特定系统中，即使CI阻遏物的暂时失活也会导致传递给细胞后代的稳定表观遗传开关，这可以被检测为Gal+（红色）菌落。导致gal表达的遗传（基因cI的突变失活）和表观遗传（基因cI产物的蛋白水解失活）机制可以区分。位于细菌染色体上的一个杂合等位基因lacZ基因与位于F'lac质粒上的另一个杂合等位基因lacZ基因之间的遗传重组，可以被检测为Lac+菌落。辐射和几种化学诱变剂在产生突变体、诱导剂和重组体方面表现出非常不同 的能力；因此，任何物理或化学试剂的剂量范围都会产生一组用于产生突变体、诱导剂和重组体的相对值，这些值是该试剂所特有的。
