Use of a Bacterial Gene Expression System for Mutation Repairing (umu system) to evaluate Damage in DNA Molecules Resulting from Exposure to an Extra Low Frequency Magnetic Field

关于极低频磁场对人体的影响，特别是对肿瘤发生的影响，虽然有很多肯定或否定的报道，但尚未得出结论。构成人体的细胞受到DNA的损伤，突变是由诱变物质或现象引起的。众所周知，突变是癌症发生的直接原因，细胞的致癌作用与DNA的分子损伤密切相关，同时基因工程也得到了长足的发展，DNA分析的实验技术已普遍应用于许多科学领域。因此，也可以利用分子生物学技术对ELFMF导入活细胞的基因水平进行研究。当细菌的DNA受到某种原因的损伤时，修复基因系统的SOS就会被表达出来，例如试图修复损伤的umu操纵子和recA基因。本研究探讨了利用UMU方法建立SOS基因表达系统的可能性，以阐明磁场暴露对DNA分子损伤所致基因突变的影响。我们将鼠伤寒沙门氏菌TA153(PSK1002)(一种去致病性的衍生菌株)暴露于ELFMF，并用UMU法检测了位于umu SOS基因操纵子下游的LacZ基因产物β-半乳糖苷酶的表达强度。实验结果表明，umu法可以有效地用于评价ELFMF对DNA分子的损伤程度，但在实验条件下，umu基因的表达强度没有显著差异。

Though there are many affirmative or negative reports on affect vicious of extremely low frequency magnetic field (ELFMF) exposure to human body, especially on the effect to oncogenesis, its conclusion has not been reached yet. Cells, which constitute the human body, suffer damage of DNA, and mutation is caused by mutagenic substances or phenomena. It is well known that mutation becomes a direct cause of cancer-developing, and there is a close relation between the oncogenesis of cells and molecular damage of DNA.In a meantime, genetic engineering has been developed remarkably, the experimental technique in DNA analysis has generally been adopted to the many fields of sciences. Therefore the gene level research of the import of the ELFMF exposure to the living cell can also be dove using molecular biological technique. When DNA of bacteria is damaged by some causes, SOS repairing genetic systems, for instance umu operon and recA genes, which intend to restore the damage, are expressed. In this study, the possibility of applying expression system of a SOS regulon by umu assay method, which clarifies the impact of a magnetic field exposure for gene mutation by a damage in DNA molecule, was examined. We exposed bacterium Salmonella typhimurium TA153(pSK1002) (a derivative strain whose pathogenicity was deleted) to ELFMF, and the intensity of the expression of an enzymatic activity of β-galactosidase which is the product of lacZ gene located downstream of the umu SOS gene operon, was examined by umu assay method with a non-exposure control. The experimental results showed that the umu assay could be effectively applied to the evaluation of damage in DNA molecules by exposure to an ELFMF.However, no significant differences were observed in the umu gene expression intensity under experimental condition.