Thermally reversible and irreversible interstrand photocrosslinking of 5-chloro-2'-deoxy-4-thiouridine modified DNA oligonucleotides.

We describe highly efficient interstrand photocrosslinking of a DNA duplex containing 5-chloro-2'-deoxy-4-thiouridine (ClSdU) in one strand, proceeding via a two-step photochemical cascade, involving the formation of a thermally reversible crosslink between ClSdU and thymidine in the target strand and its subsequent conversion to a thermally stable fluorescent crosslink. These results show that ClSdU has great potential to be a valuable DNA photo-crosslinking reagent for chemical biology applications.