Helicase-contrahelicase interaction and the mechanism of termination of DNA replication.

Termination of DNA replication at a sequence-specific replication terminus is potentiated by the binding of the replication terminator protein (RTP) to the terminus sequence, causing polar arrest of the replicative helicase (contrahelicase activity). Two alternative models have been proposed to explain the mechanism of replication fork arrest. In the first model, the RTP-terminus DNA interaction simply imposes a polar barrier to helicase movement without involving any specific interaction between the helicase and the terminator proteins. The second model proposes that there is a specific interaction between the two proteins, and that the DNA-protein interaction both restricts the fork arrest to the replication terminus and determines the polarity of the process. The evidence presented in this paper strongly supports the second model.