Described are methods of detecting modified nucleotide bases in a DNA sample using specific DNA glycosylases to excise target modified bases. DNA molecules are then labeled using a DNA polymerase lacking 3.fwdarw.5 exo-nuclease activity and strand displacement activity. The methods can be used to detect epigenetic changes and DNA damage. Provided are methods for diagnosing a disease or condition, determining risk of a disease or condition, identifying appropriate treatment, monitoring effectiveness of treatment, and monitoring side effects of treatment in subjects based on detection of modified bases. Also provided are methods for determining environmental exposure, or an environmental exposure time, of a biological sample containing DNA. Also provided are kits, systems, and devices for performing the described methods.

Among other things, a method for performing multiple enzyme reactions in a single tube is provided. In some embodiments, the method may comprise producing a reaction mix comprising a thermolabile UDG, an AP lyase and DNA fragments that comprise one or more uracil residues, incubating the reaction mix at a relatively low temperature to cleave fragments at the one or more uracil residues, raising the temperature of the reaction mix to a relatively high temperature to inactivate the thermolabile UDG; and deaminating the fragments, thereby converting any cytosine in the fragments of DNA to uracil.

Among other things, a method for performing multiple enzyme reactions in a single tube is provided. In some embodiments, the method may comprise producing a reaction mix comprising a thermolabile UDG, an AP lyase and DNA fragments that comprise one or more uracil residues, incubating the reaction mix at a relatively low temperature to cleave fragments at the one or more uracil residues, raising the temperature of the reaction mix to a relatively high temperature to inactivate the thermolabile UDG; and deaminating the fragments, thereby converting any cytosine in the fragments of DNA to uracil.