Fig. 6.

Examples of unidirectional late-stage replication. Parental DNA is black, and nascent DNA is green. (Left) The end of prokaryotic chromosomal replication is depicted. The fork coming from the right encounters a ter site and stalls. The fork from the left must complete replication by proceeding unidirectionally. (Right) Replication of a eukaryotic chromosome is shown. Unevenly spaced origins initiate bidirectionally, but closely spaced forks converge and terminate, and their divergent counterparts must complete replication unidirectionally.