HELICASE-CONTRAHELICASE INTERACTION AND THE MECHANISM OF TERMINATION OF DNA-REPLICATION

Termination of DNA replication at a sequence-specific replication term inus is potentiated by the binding of the replication terminator prote in (RTP) to the terminus sequence, causing polar arrest of the replica tive helicase (contrahelicase activity). Two alternative models have b een proposed to explain the mechanism of replication fork arrest. In t he first model, the RTP-terminus DNA interaction simply imposes a pola r barrier to helicase movement without involving any specific interact ion between the helicase and the terminator proteins. The second model proposes that there is a specific interaction between the two protein s, and that the DNA-protein interaction both restricts the fork arrest to the replication terminus and determines the polarity of the proces s. The evidence presented in this paper strongly supports the second m odel.