Dynamics of association of origins of DNA replication with the nuclear matrix during the cell cycle

DNA of replication foci attached to the nuclear matrix was isolated from Chinese hamster ovary cells and human HeLa cells synchronized at different stages of the G(1) and S phases of the cell cycle. The abundance of sequences from dihydrofolate reductase ori-beta and the beta -globin replicator was determined in matrix-attached DNA. The results show that matrix-attached DNA isolated from cells in late G(1) phase was enriched in origin sequences in comparison with matrix-attached DNA from early G(1) phase cells. The concentration of the early firing ori-beta in DNA attached to the matrix decreased in early S phase, while the late firing beta -globin origin remained attached until late S phase. We conclude that replication origins associate with the nuclear matrix in late G(1) phase and dissociate after initiation of DNA replication in S phase.