Editing SOS response (section)

==Genotoxicity testing==
[[Image:Genotoxic_Damage.png|300px|right|thumb|Overview of the use of the SOS response for 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, thereby 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.<ref>{{cite journal |last1=Quillardet |first1=Philippe |last2=Hofnung |first2=Maurice |title=The SOS chromotest: a review |journal=Mutation Research/Reviews in Genetic Toxicology |date=October 1993 |volume=297 |issue=3 |pages=235–279 |doi=10.1016/0165-1110(93)90019-J |pmid=7692273}}</ref> 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.<ref>{{cite journal |last1=Quillardet |first1=Philippe |last2=de Bellecombe |first2=Christine |last3=Hofnung |first3=Maurice |title=The SOS Chromotest, a colorimetric bacterial assay for genotoxins: validation study with 83 compounds |journal=Mutation Research/Environmental Mutagenesis and Related Subjects |date=June 1985 |volume=147 |issue=3 |pages=79–95 |doi=10.1016/0165-1161(85)90021-4 |pmid=3923333}}</ref>