The non-random distribution of UV-induced photoproducts in the nuclear matrix and non-matrix DNA fractions

The formation of UV-induced photoproducts in the chromatin fractions of human lymphocytes was studied by 32P-postlabeling. A higher level of DNA lesions was found in the matrix-attached DNA fraction as compared to non-matrix DNA of irradiated cells (about 150 and 110 adducts per 106 nucleotides, respectively, at a 500 J/m2 254 nm-UV dose). Formation of photoproducts in a MAR (matrix attached region) sequence from the mouse kappa immunoglobulin gene irradiated in vitro was examined as well. The MAR sequence showed a two-fold higher level of adducts as compared to non-MAR DNA. The effect of photoproducts on complex-formation between MAR DNA and proteins of the nuclear matrix was studied in vitro. The amount of UV-induced adducts was 1.5-fold higher in matrix-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 nuclear matrix proteins.