Effects of Adducts on Tm

Synonyms

Changes in DNA melting curves

Definition

Thermal melting of DNA involves the breaking of double-stranded DNA into single strands, defined by the “melting temperature” (T _m), the temperature at which one-half of the DNA is melted. Modification of DNA by chemical damage often changes the thermodynamics of the process, and the alteration is a part of the characterization of the damage.

Discussion

The presence of DNA adducts often disrupts normal pairing of DNA bases (see “Modes of DNA Base Pairing”), and the melting temperature (T _m) of a double-stranded oligonucleotide is decreased.

The procedure involves use of a double-stranded oligonucleotide, usually 12–18 bases in length. If the oligonucleotide is too short, it will not anneal, even at low temperature. If the oligonucleotide is too long, then the difference imposed by the adduct may not be prominent enough to observe. The presence of high salt increases the T _m, so experiments are often done in 0.5 M NaCl.

The usual...