Activation occurs during a specific phase of the cell division cycle, the S phase.
Activation is limited to only once per cell cycle.
Duplication of the DNA starts at sites called replication origins. Each chromosome has multiple replication origins and different types of origins are activated at different specific times. Both activation and completion of chromosome replication are coordinated with chromosome segregation in a dividing cell, maintaining a precise replica of parental genetic information in the progeny cells. Activation of replication origins is mediated by a novel type of genetic element. A DUE serves to facilitate the opening of the double helix during initiation of replication.