8-Methoxypsoralen photoadduct formation in complementary oligonucleotides containing a cross-linkable site

The complete profile of 8-methoxypsoralen photoadduct formation in complementary oligonucleotides (5'-GAGTATGAG and 5'-CATAC) has been determined. Equimolar solutions of the oligonucleotides were irradiated at 4 degrees C in order to stabilize the mini-double helix. Photomodified oligonucleotides were separated by reversed phase chromatography on a Vydac C4 column. Photoadduct formation favored the 5'TAT site in the 9mer over the 5'ATA site in the 5mer by a factor of two. Split-dose studies showed that the monoadducts formed on GAGTATGAG were preferentially converted to cross-links by an additional UVA exposure.