PHOTOLYTIC COVALENT BINDING OF INDOLEACRYLIC ACID TO DNA*

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Abstract
E-.beta.-Indol-3-ylacrylic acid (IA), radiolabelled at the 2 position with 14C, and calf thymus DNA have been irradiated with UV light (.lambda. > 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 A 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 photocycloadduct 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.