THE NONRANDOM DISTRIBUTION OF UV-INDUCED PHOTOPRODUCTS IN THE NUCLEARMATRIX AND NON-MATRIX DNA FRACTIONS

The formation of UV-induced photoproducts in the chromatin fractions o f human lymphocytes was studied by P-32-post-_ labeling. A higher leve l of DNA lesions was found in the matrix-attached DNA fraction as comp ared to non-matrix DNA of irradiated cells (about 150 and 110 adducts per 10(6) nucleotides, respectively, at a 500 J/m(2) 254 nm-UV dose). Formation of photoproducts in a MAR (matrix attached region) sequence from the mouse kappa immunoglobulin gene irradiated in vitro was exami ned as well, The MAR sequence showed a two-fold higher level of adduct s as compared to non-MAR DNA. The effect of photoproducts on complex-f ormation between MAR DNA and proteins of the nuclear matrix was studie d in vitro. The amount of UV-induced adducts was 1.5-fold higher in ma trix-bound fraction as compared to non-fractionated DNA (and five-fold higher as compared to unbound fraction), which possibly resulted from preferential binding of lesion-containing DNA fragments to the nuclea r matrix proteins.