The term host cell reactivation or HCR was first used to describe the survival of UV-irradiated bacteriophages, that were transfected to UV-pretreated cells. This phenomenon was first thought to be the result of homologous recombination between both bacteria and phage, but later recognized as enzymatic repair. Modifications of the assay were later developed, using transient expression plasmid DNA vectors on immortalized fibroblasts, and lately on human

lymphocyte A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic ad ...

s. The HCR assay known also as plasmid reactivation assay, indirectly monitors cellular transcriptional repair system, that is activated by the transcriptional-inhibited damage inflicted by UV-Radiation into the

plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; how ...

. Given that UV-induced DNA damage is used as

mutagen In genetics, a mutagen is a physical or chemical agent that permanently changes nucleic acid, genetic material, usually DNA, in an organism and thus increases the frequency of mutations above the natural background level. As many mutations can ca ...

, the cell uses nucleotide excision repair

NER NER may refer to: * New European Recordings, a record label * ISO 3166-1 three letter code for Niger * Named entity recognition, a text processing task that identifies certain words as belonging to one class or another * Northeast Regional, an Amtr ...

pathway, that is activated by distortion in the DNA helix. The Host-Cell Reactivation Assay or HCR is a technique used to measure the

DNA repair DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA dam ...

capacity of cell of a particular DNA alteration. In the HCR assay the ability of an intact cell to repair exogenous DNA is measuredMcCready, S. (2014). An Immunoassay for Measuring Repair of DNA. In P. Keohavong & S. G. Grant (Eds.), Molecular Toxicology Protocols (Vol. 1105, pp. 551–564). Humana Press. The host cell is

transfected Transfection is the process of deliberately introducing naked or purified nucleic acids into eukaryotic cells. It may also refer to other methods and cell types, although other terms are often preferred: "transformation" is typically used to desc ...

with a damaged

containing a

reporter gene In molecular biology, a reporter gene (often simply reporter) is a gene that researchers attach to a regulatory sequence of another gene of interest in bacteria, cell culture, animals or plants. Such genes are called reporters because the charac ...

, usually

luciferase Luciferase is a generic term for the class of oxidative enzymes that produce bioluminescence, and is usually distinguished from a photoprotein. The name was first used by Raphaël Dubois who invented the words ''luciferin'' and ''luciferase'', ...

, which has been deactivated due to the damage. The ability of the cell to repair the damage in the plasmid, after it has been introduced to the cell, allows the reporter gene to be reactivated. Earlier versions of this assay were based on the chloramphenicol acetyltransferas
(CAT)
gene, but the version of the assay using luciferase as

is as much as 100-fold more sensitive.

References

{{Reflist Molecular biology Laboratory techniques DNA repair Mutation

See also

References