PHOTO-CROSS-LINKING OF 5-IODOURACIL SUBSTITUTED RNA AND DNA TO PROTEINS

5-Iodouracil-substituted RNA and DNA were crosslinked regiospecificall y to associated proteins in yields of 70 to 94% of bound nucleic acid. Irradiation of the iodouracil chromophore with monochromatic, long-wa velength ultraviolet radiation (325 nanometers) eliminates excitation of other nucleic acid and protein chromophores. The combination of hig h crosslinking yields, excellent specificity, and elimination of photo damage to other chromophores represents an important advance toward th e precise identification of contacts in nucleoprotein complexes.