Replication terminator protein

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Replication terminator protein (RTP) helps Bacillus stop DNA replication. It binds DNA with a winged-helix shape and forms a dimer (two RTP molecules) held together by hydrogen bonds. The dimer is symmetric when not bound to DNA, but becomes asymmetric when it binds. Its action is polar: it blocks the replication fork moving in one direction while allowing the fork from the opposite direction to continue.

Each RTP dimer binds to a 20-base-pair DNA site. The chromosome’s termination region (ter) contains two dimer-binding sites, A and B, that overlap by 3 base pairs. The A site has a higher affinity for RTP. When a dimer binds to the A site, it changes the shape of the B site to make it easier for another dimer to bind there.

Earlier thinking (before 2006) was that RTP stopped replication simply by clamping onto DNA. A 2006 study showed that RTP also interacts with the replication machinery itself, helping to terminate replication.