Association of putative origins of replication with the nuclear matrix in normal human fibroblasts

Several metabolic processes, such as DNA organization and replication, transcription, and RNA processing are closely associated with the nuclear matrix. Nuclear matrix attachment regions are nucleotide sequences holding DNA tightly complexed with the nuclear scaffold and are resistant to extractions with detergents and high salt solutions. The role of matrix attachment regions in DNA replication has not been completely clarified, but they have been identified in close association with origins of replication in mammalian cells. We isolated nuclear matrix-associated DNA from normal human fibroblasts synchronized to different phases of the cell cycle and cloned compatible fragments into pUC19. We tested the homology of a fraction of the available clones to DNA replicated at the beginning of the S phase in human fibroblasts. We confirmed that nuclear matrix-associated DNA isolated from cells in G0 and G1 phases of the cell cycle contains sequences that are among the earliest replicated regions in the human genome. This finding supports the hypothesis that matrix attachment regions in human DNA are located in close proximity to origins of DNA replication.