Figure 1.

Initiation of replication at multiple origins in Escherichia coli and Schizosaccharomyces pombe. Origins that have not yet initiated are shown in green, whereas those initiated or passively replicated are shown in red. The E. coli cell is fast-growing with S + G2 phases spanning more than two generation times. Consequently, initiations occur in synchrony at four cellular origins. For simplicity, only one chromosome with six autonomously replicating sequences is shown in the S. pombe cell. Four of these are firing, whereas two are being passively replicated.