The molecular mechanisms mediating eukaryotic replication termination and pausing remain largely unknown. Here we present the molecular characterization of Rtf1 that mediates site-specific replication termination at the polar Schizosaccharomyces pombe barrier RTS1. We show that Rtf1 possesses two chimeric myb/SANT domains: one is able to interact with the repeated motifs encoded by the RTS1 element as well as the elements enhancer region, while the other shows only a weak DNA binding activity. In addition we show that the C-terminal tail of Rtf1 mediates self-interaction, and deletion of this tail has a dominant phenotype. Finally, we identify a point mutation in Rtf1 domain I that converts the RTS1 element into a replication barrier of the opposite polarity. Together our data establish that multiple protein DNA and protein-protein interactions between Rtf1 molecules and both the repeated motifs and the enhancer region of RTS1 are required for site-specific termination at the RTS1 element.
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