CELL-CYCLE MODULATION OF PROTEIN-DNA INTERACTIONS AT A HUMAN REPLICATION ORIGIN

We followed the variations of protein-DNA interactions occurring in vi vo over the early firing replication origin located near the human lam in B2 gene, in IMR-90 cells synchronized in different moments of the c ell cycle, In G(0) phase cells no protection is present; as the cells progress in G(1) phase an extended footprint covering over 100 bp appe ars, particularly marked at the G(1)/S border. As the cells enter S ph ase the protection shrinks to 70 bp and remains unchanged throughout t his phase. In mitosis the protection totally disappears, only to reapp ear in its extended form as the cells move into the next G(1). These v ariations are reminiscent of those corresponding to the formation of t he pre-and post-replicative complexes described in yeast and Xenopus c ells.