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The history and mechanism of photolyase: How bacteria recover after sunburn

OTHER VIDEOS YOU MIGHT LIKE: • An a-MAIZE-ing story about family, corn and sweet, sweet evolution -    • An a-MAIZE-ing story about family, co...   • Capillary coup! The birth of the Southern blot -    • Capillary coup! The birth of the Sout...   • Immunity genes also control a dog’s coat colour? -    • Immunity genes also control a dog’s c...   Have you ever wondered if bacteria could get sunburnt? Well, sorry to disappoint, but they can’t. However, exposure to UV radiation can cause the formation of pyrimidine dimers in their DNA which can lead to mutations. But how do they repair this? Let me introduce you to a scientist called Albert Kelner, who published a study all the way back in 1949. In this study Kelner irradiated E. coli with UV light. Whilst usually causing mass fatality amongst bacteria, he found exposing irradiated bacteria to light after their nasty sunbath would result in a much higher survival rate. Intrigued, he also found that the light-treatment would lead to less mutations as well. He called this phenomenon photoreactivation. After less than a decade, it was concluded that photoreactivation was likely driven by enzymes. As the century progressed, so did our understanding of photoreactivation. In the 70s scientists were finally able to purify and name the enzyme responsible: photolyase. With purification, scientists could finally get on with figuring out how this important enzyme worked. We found out that the action of photolyase is dependent on a molecule called flavin adenine dinucleotide (FAD). Photolyase can recognise pyrimidine dimers and bind to them. When a photon with a blue-light wavelength strikes the photolyase, this excites an electron in the FAD, which is transferred to the pyrimidine dimer, destabilising its bond, causing it to break apart. It turns out this is crucial to protecting bacteria. If the DNA replicates when one of these dimers is present, the DNA polymerase will be blocked, leading to single stranded sections of DNA. If enough of these single stranded sections accumulate it will trigger an SOS-response. Whilst repairing the DNA, the SOS response can also cause mutations. That’s why photolyase is so important, as it stops the SOS response from being triggered. Creator: Sam Morris References: Effect of visible light on the recovery of Streptomyces griseus conidia from ultra-violet irradiation injury. Kelner A.Proc Natl Acad Sci U S A. 1949 Feb;35(2):73-9. doi: 10.1073/pnas.35.2.73. Photoreactivation of ultraviolet-irradiated Escherichia coli, with special reference to the dose-reduction principle and to ultraviolet-induced mutation. Kelner A. J Bacteriol. 1949 Oct;58(4):511-22. doi: 10.1128/jb.58.4.511-522.1949. Photoreactivation in vitro of ultraviolet-inactivated Hemophilus influenzae transforming factor. Rupert CS, Goodgal SH, Herriott RM. J Gen Physiol. 1958 Jan 20;41(3):451-71. doi: 10.1085/jgp.41.3.451. Purification of a blue-green algal deoxyribonucleic acid photoreactivating enzyme. An enzyme requiring light as a physical cofactor to perform its catalytic function. Saito N, Werbin H. Biochemistry. 1970 June 1;9(13): 2610-2620. doi: 10.1021/bi00815a008 Action mechanism of Escherichia coli DNA photolyase. III. Photolysis of the enzyme-substrate complex and the absolute action spectrum. Sancar GB, Jorns MS, Payne G, Fluke DJ, Rupert CS, Sancar A. J Biol Chem. 1987 Jan 5;262(1):492-8. Purification and characterization of an inducible Escherichia coli DNA polymerase capable of insertion and bypass at abasic lesions in DNA. Bonner CA, Randall SK, Rayssiguier C, Radman M, Eritja R, Kaplan BE, McEntee K, Goodman MF. J Biol Chem. 1988 Dec 15;263(35):18946-52. Nature of the SOS-inducing signal in Escherichia coli. The involvement of DNA replication. Sassanfar M, Roberts JW. J Mol Biol. 1990 Mar 5;212(1):79-96. doi: 10.1016/0022-2836(90)90306-7. UmuD'(2)C is an error-prone DNA polymerase, Escherichia coli pol V. Tang M, Shen X, Frank EG, O'Donnell M, Woodgate R, Goodman MF. Proc Natl Acad Sci U S A. 1999 Aug 3;96(16):8919-24. doi: 10.1073/pnas.96.16.8919. A 9‐month, randomized, assessor‐blinded, parallel‐group study to evaluate clinical effects of film‐forming medical devices containing photolyase and sun filters in the treatment of field cancerization compared with sunscreen in patients after successful photodynamic therapy for actinic keratosis. L Eibenschutz, V Silipo, P De Simone, P. Buccini, A Ferrari, A Carbone, C Catricalà. Br J Dermatol. 2016 Dec 1;175(6): 1391–3. doi: doi.org/10.1111/bjd.14721.