ORGANIC-PHOTOCHEMISTRY .81. PHOTOLYTIC COVALENT BINDING OF INDOLEACRYLIC ACID TO DNA

Abstract— E‐β‐IndoI‐3‐ylacrylic acid (IA), radiolabeled at the 2 position with l+C, and calf thymus DNA have been irradiated with UV light (Λ > 280 nm) in phosphate buffer (pH 7.0). Re‐isolation of the DNA indicates covalent binding of IA at levels of up to 295 nmol IA/mg native DNA (0.097 IA/ base). Binding is observed for both native and heat denatured DNA, but is more efficient with the latter. Quantum efficiencies of 2.60 times 10−5 and 2.30 times 10 −4 mol IA bound to native DNA/mol photon absorbed have been measured at 308 and 266 nm, respectively. Studies with the four polyribonucleotides indicate a strong preference for binding to poly[U]. Photolysis of either untreated or enzymatically degraded labeled native DNA with 254 nm light leads to the reformation of IA, and a 2 + 2 photocy‐cloadduct of IA and thymidine has been isolated and characterized and matched by HPLC to a DNA derived adduct. Equilibrium dialysis studies provide no evidence for preassociation of IA to DNA. Copyright © 1990, Wiley Blackwell. All rights reserved