Eukaryotic DNA is known to be synthesized via replication complexes that are fixed to proteinaceous nuclear complex. We investigated whether the binding of parental DNA to the nuclear matrix is affected by ultraviolet(UV) light in mouse LP1-1 cells. The matrix-binding of parental DNA as determined by DNase-digestion of halo structures, markedly increased to 7-fold of control at 2hr after irradiation (10J/m2) and then decreased as a time dependent manner. These enhanced binding of parental DNA by UV light may suggest that the newly activated replication origins bind transiently to the nuclear matrix. To examine that these enhanced bindings reflect the activation of new replication origin, we determined the rate of DNA synthesis and the sizes of newly replicated DNA. The weight average molecular weights (Mw) of nascent DNA were still smaller than that of control at 2hr after UV-irradiation, while the rate of DNA synthesis completely recovered during the same time period. These results indicate that the new replication origins were activated by UV-irradiation in order to replicate the long-lived unreplicated regions (LLUR) produced by UV lesions in LP1-1 cells.