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 Ch inese hamster ovary cells and human HeLa cells synchronized at different st ages 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 DN A isolated from cells in late G(1) phase was enriched in origin sequences i n comparison with matrix-attached DNA from early G(1) phase cells. The conc entration of the early firing ori-beta in DNA attached to the matrix decrea sed in early S phase, while the late firing beta -globin origin remained at tached until late S phase. We conclude that replication origins associate w ith the nuclear matrix in late G(1) phase and dissociate after initiation o f DNA replication in S phase.