SOS Response - Genotoxicity Testing

Genotoxicity Testing

In Escherichia coli, different classes of DNA-damaging agents can initiate the SOS response, as described above. Taking advantage of an operon fusion placing the lac operon (responsible for producing beta-galactosidase, a protein which degrades lactose) under the control of an SOS-related protein, a simple colorimetric assay for genotoxicity is possible. A lactose analog is added to the bacteria, which is then degraded by beta-galactosidase, there-by producing a colored compound which can be measured quantitatively through spectrophotometry). The degree of color development is an indirect measure of the beta-galactosidase produced, which itself is directly related to the amount of DNA damage.

The E. coli are further modified in order to have a number of mutations including a uvrA mutation which renders the strain deficient in excision repair, increasing the response to certain DNA-damaging agents, as well as an rfa mutation, which renders the bacteria lipopolysaccharide-deficient, allowing better diffusion of certain chemicals into the cell in order to induce the SOS response. Commercial kits which measures the primary response of the E. coli cell to genetic damage are available and may be highly correlated with the Ames Test for certain materials.