Fig. 1. Schematic representation of Lac-Phe-Ter chromosome. (A) Chromosome on which replication is blocked at Terphe and Terlac. (B) Cleavage of both leading and lagging strands. (C) Cleavage of two strands of the same polarity (leading or lagging strands), at both Ter sites. (D) DNA replication initiated at oriC and progressing to Terphe and Terlac. Natural terminators are symbolized by gray indented rectangles, and Terphe and Terlac by white indented rectangles. The chromosome origins (oriC) are shown as small circles. Each line represents double-stranded DNA. Cleavage sites are indicated by black arrows.