Mechanisms of separation of the complementary strands of DNA during replication

This article is a perspective on the separation of the complementary strand s of DNA during replication. Given the challenges of DNA strand separation and its vital importance, it is not surprising that cells have developed ma ny strategies for promoting unlinking. We summarize seven different factors that contribute to strand separation and chromosome segregation. These are : (1) supercoiling promotes unlinking by condensation of DNA; (2) unlinking takes place throughout a replicating domain by the complementary action of topoisomerases on precatenanes and supercoils; (3) topological domains iso late the events near the replication fork and permit the supercoiling-depen dent condensation of partially replicated DNA; (4) type-II topoisomerases u se ATP to actively unlink DNA past the equilibrium position; (5) the effect ive DNA concentration in vivo is less than the global DNA concentration; (6 ) mechanical forces help unlink chromosomes; and (7) site-specific recombin ation promotes unlinking at the termination of replication by resolving cir cular dimeric chromosomes.