Abstract
DNA glycosylases function to remove endogenous and exogenous base damageand thus contribute to the maintenance of genomic integrity. This function gains clinicalrelevance when base mispairs introduced by chemotherapy or radiosensitizing drugsbecome their substrate. This report describes the action of DNA glycosylases on themispairs generated by iododeoxyuridine (IUdR) – a radiosensitizer. A non-radioactivefluorescent dye-based in vitro glycosylase assay was employed to quantitatively measurethe enzymatic activities of functionally related DNA glycosylases on IUdR generatedmispairs including G:IU and A:IU. Thymine DNA glycosylase (TDG) and methylbinding domain protein 4 (MBD4/MED1) are found to act on G:IU (but not A:IU)mispairs and are functionally complementary to each other. However, uracil DNAglycosylase (UDG) does not show any activity on these mispairs. The methyl bindingdomain of MBD4/MED1 was found to specifically inhibit the activity of MBD4/MED1as well as the glycosylase domain, when the G:IU mispairs were located in a methylatedCpG context. However, inhibition of TDG activity on methylated G:IU mispairs by themethyl binding domain was not observed.
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