Chemical modification
During interstrand cross-linking, two strands of the DNA molecule become
covalently linked preventing full separation of DNA strands using heat.
This can be facilitated by UV-A light and the presence of intercalating
agents. Interstrand cross-linking makes DNA inaccessible to PCR
detection, but this is not degradation per se. We mention this
reaction because at this time we cannot differentiate non-detection
resulting from true degradation versus interstrand cross-linking using
PCR.