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.
Read more about this topic: SOS Response
Famous quotes containing the word testing:
“Today so much rebellion is aimless and demoralizing precisely because children have no values to challenge. Teenage rebellion is a testing process in which young people try out various values in order to make them their own. But during those years of trial, error, embarrassment, a child needs family standards to fall back on, reliable habits of thought and feeling that provide security and protection.”
—Neil Kurshan (20th century)