Termination of replication involves binding of Tus protein to
E. coli chromosome contains terminus region opposite oriC harboring ten ter sites each 23 base pairs oriented to trap forks arriving from either direction. Tus protein binds ter as monomer and when replication fork helicase DnaB encounters Tus-ter complex in non-permissive orientation, Tus interacts with DnaB blocking unwinding and arresting fork progression. This polar barrier prevents over-replication beyond terminus and ensures fork fusion within terminus region. OriC functions in initiation, DUE unwinds initially, but Tus-ter provides authentic termination checkpoint enforcing completion.
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 11: Tus binding to ter sites terminates replication fork progression