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The Umu Chromotest, first developed and published by Oda et al., is a biological assay (bioassay) to assess the genotoxic potential of chemical compounds. It is based on the ability of DNA-damaging agents to induce the expression of the umu operon. In connection with the damage inducible (din) genes recA, lexA and umuD, the umuC gene is essentially involved in bacterial mutagenesis through the SOS response. This test uses an operon fusion placing the lac operon (responsible for producing β-galactosidase, a protein which degrades lactose) under the control of the umu-related proteins. A simple colorimetric test is possible by adding a lactose analog which is degraded by β-galactosidase, producing a colored compound which can be measured quantitatively through spectrophotometry. The degree of color development is an indirect measure of the β-galactosidase produced, which itself is directly related to the amount of DNA damage. The Umu Chromotest has the added advantage of having its procedure codified under ISO 13829 "Water Quality- Determination of genotoxicity of water and waste water using the umu-test". Although genotoxicity cannot be linked directly to the development of cancer in humans, a strong correlation between genotoxic effects in bacteria and their mutagenic and tumor-initiating properties in mammals has been shown to exist. ==Theory== ''Salmonella typhimurium'' TA 1535 (1002 ) bacteria are exposed to potentially genotoxic test compounds in a 96-well microplate. If genotoxic lesions are produced in the bacterial genome, the umuC gene is induced as part of the general SOS response. The plasmid pSK1002 contains the umuC gene fused to the lacZ reporter gene, much like the fusion in the SOS Chromotest. The induction of the umuC-gene is thus a measure for the genotoxic potential of the sample. Since the umuC-gene is fused with the lacZ-gene for β-galactosidase, the induction of the umuC-gene can be easily assessed by determination of the β-galactosidase activity, measured by the conversion of a colorless ONPG substrate (o-nitrophenyl-β-D-galactopyranoside) to the yellow product o-nitrophenyl by the lacZ-encoded B-galactosidase. As the SOS response is a general response to genotoxic lesions, one strain of S. typhimurium with the appropriate reporter gene construct is sufficient to identify all classes of bacterial genotoxins. As with other bacterial genotoxicity and mutagenicity assays, compounds requiring metabolic activation for activity can be investigated with the addition of S9 microsomal rat liver extract. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Umu Chromotest」の詳細全文を読む スポンサード リンク
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