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AlkB and ABH prefer singlestranded DNA or RNA substrates while ABH preferentially acts on dsDNA. ABH and ABH knockout mice as well as double knockout mice are viable and do not show   an obvious phenotype.ABH, but not ABH, deficient mice accumulate methyladenine lesions in the absence of exogenous methylating agents.Transgenic mice were initiated with a single subthreshold dose of MNU followed by treatment with TPA twice a week.Moreover, a flexible hairpin was identified which is probably involved in substrate binding.In eukaryotes, the yield and distribution of DNA lesions may be influenced by a higherorder DNA structure as CPD lesions are found predominantly in nucleosomal DNA. Despite the fact that most organisms have acquired the nucleotide excision repair system for removal of helixdistorting lesions and other bulky DNA adducts, highly specific direct damage reversal mechanisms exist for the three types of photoproducts.Spore formation involves the generation of a forespore within the bacterial cell.During this process, SP lyase is synthesized and packed ready for use in the forespore.Electron transfer from the cluster to SAM generates a free deoxyadenosyl radical, while the methionine part remains bound to the cluster. When these <a href="https://www.ncbi.nlm.nih.gov/pubmed/15456537">buy Montelukast</a> photolyase UVDNA complexes are illuminated with visible or nearUV light, photon energy is used to repair DNA damage.Absorbtion of visible light requires the presence of a chromophoric group.In fact, photolyases contain two, functionally different, chromophoric cofactors.The first chromophore, FAD, acts as the photochemical reaction center.Various FAD redox states have been found in purified photolyases: oxidized FAD, the halfreduced neutral semiquinone radical FADH, and the deprotonated fully reduced form FADH. It is possible, however, to convert the inactive forms of FAD into FADH by photoreduction where an electron is transferred from an exogenous photoreductor through a chain of three tryptophans to FAD. The second chromophore, which is either reduced folate, acts as an auxiliary lightharvesting antenna.The presence of a second chromophore is not an absolute requirement for activity, as apophotolyases lacking this chromophore are still able to repair UV lesions.Its presence, however, improves the efficiency of photolyase considerably.Photolyases are specific for either CPD or PP lesions.Yet the reaction mechanisms are largely the same: shuttling an electron to the lesion in order to destabilize it.The driving force for this reaction is the energy acquired by the chromophores by absorption of a photon, yielding excited fully reduced FADH PP photolyases a lightindependent step precedes electron transfer.Binding of the PP lesion to photolyase induces a rearrangement and an oxetanering is formed. Once a lesion radical is formed, the bond between the pyrimidine rings are broken and finally an electron is transferred back to the catalytic cofactor.A similar structure was obtained for the core region of cryptochrome. A photolyasesubstrate complex structure clearly shows the dimer lesion completely flipped out of the DNA. For a detailed description of reaction mechanism and structures see a recent review. Based on these structures a reaction mechanism has been proposed without an oxetane intermediate.Phylogenetic analysis of the amino acid sequence of the core domain of all members of the photolyase family indicates a clear relationship.

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