Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 26 (3), 249-61

The Comet Assay for DNA Damage and Repair: Principles, Applications, and Limitations


The Comet Assay for DNA Damage and Repair: Principles, Applications, and Limitations

Andrew R Collins. Mol Biotechnol.


The comet assay (single-cell gel electrophoresis) is a simple method for measuring deoxyribonucleic acid (DNA) strand breaks in eukaryotic cells. Cells embedded in agarose on a microscope slide are lysed with detergent and high salt to form nucleoids containing supercoiled loops of DNA linked to the nuclear matrix. Electrophoresis at high pH results in structures resembling comets, observed by fluorescence microscopy; the intensity of the comet tail relative to the head reflects the number of DNA breaks. The likely basis for this is that loops containing a break lose their supercoiling and become free to extend toward the anode. The assay has applications in testing novel chemicals for genotoxicity, monitoring environmental contamination with genotoxins, human biomonitoring and molecular epidemiology, and fundamental research in DNA damage and repair. The sensitivity and specificity of the assay are greatly enhanced if the nucleoids are incubated with bacterial repair endonucleases that recognize specific kinds of damage in the DNA and convert lesions to DNA breaks, increasing the amount of DNA in the comet tail. DNA repair can be monitored by incubating cells after treatment with damaging agent and measuring the damage remaining at intervals. Alternatively, the repair activity in a cell extract can be measured by incubating it with nucleoids containing specific damage.

Similar articles

See all similar articles

Cited by 393 PubMed Central articles

See all "Cited by" articles


    1. Eur J Nutr. 1999 Feb;38(1):28-34 - PubMed
    1. J Cell Sci. 1976 Nov;22(2):303-24 - PubMed
    1. Mutagenesis. 2002 Nov;17(6):495-507 - PubMed
    1. Biochem Biophys Res Commun. 1984 Aug 30;123(1):291-8 - PubMed
    1. Exp Cell Res. 1997 May 1;232(2):407-11 - PubMed

LinkOut - more resources