Photochemical cross-linking of protein and DNA in chromatin. Synthesis and application of a photosensitive cleavable derivative of 9-aminoacridine with two photoprobes connected through a disulphide-containing linker

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Abstract
A novel cleavable photo-cross-linking reagent, N-(2-methoxy-6-azidoacridin-9-yl)-N''-(4-azidobenzoyl)cystamine, for analysis of protein-nucleic acid interactions, was synthesized. The reagent contains 2 photosensitive groups that can be activated sequentially. The azidoacridinyl moiety is sensitive to UV and visible light (.lambda. .ltoreq. 450 nm), whereas the azidobenzoyl part needs higher-energy light (.lambda. .ltoreq. 350 nm). Furthermore, the disulfide bridge connecting the 2 photoactive groups can be cleaved by reduction with mercaptans. The reagent induces cleavable cross-links between all 5 major histones and DNA in chromatin from Ehrlich ascites cells on activation with long-wavelength UV light (.lambda. > 300 nm) at an efficiency of .apprx. 3% of the added reagent.