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

虽然对极低频磁场（ELFMF）对人体的影响，特别是对肿瘤的影响有许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，细胞的癌变与DNA的分子损伤有着密切的关系。与此同时，基因工程得到了显著的发展，DNA分析的实验技术已普遍应用于许多科学领域。因此，利用分子生物学技术，也可以在基因水平上研究极低频电磁场对活细胞的影响。当细菌的DNA受到某些原因的损伤时，会表达SOS修复基因系统，如umu操纵子和recA基因，这些基因旨在修复损伤。本研究通过umu法研究了SOS调控子表达系统应用的可能性，阐明了磁场暴露对DNA分子损伤基因突变的影响。我们将鼠伤寒沙门菌TA153(pSK1002)（一株致病性被删除的衍生菌株）暴露于ELFMF中，用umu法检测了位于umu SOS基因操纵子下游的lacZ基因产物β-半乳糖苷酶活性的表达强度，并进行了非暴露对照。实验结果表明，umu法可有效地用于评价DNA分子在极低频电磁场下的损伤。然而，在实验条件下，umu基因表达强度无显著差异。

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.