Replication termination factor which is a component of the elongating replisome. Required for ATR pathway signaling upon DNA damage and has a positive activity during DNA replication. Might function to facilitate fork pausing at replication fork barriers like the rDNA. May be globally required to stimulate ATR signaling after the fork stalls or encounters a lesion. Interacts with nascent DNA. Interacts with DDI2; probably also interacts with DDI1. Localizes at the replication fork. Undergoes proteasomal degradation, via DDI1 and DDI2. Removal from stalled replisomes and degradation are required for genome stability. Belongs to the rtf2 family.