Fig. 7: A model showing the establishment of IZ and RT in WT cells and their loss in RIF1-KO cells.

In WT cells, RIF1-PP1 is localised in heterochromatin from G1 to early S phase, counterbalancing MCM-DH phosphorylation by DDK. The limiting firing factor, TRESLIN-MTBP, is specifically recruited to phosphorylated MCM-DH at intergenic regions, leading to RT formation. In RIF1-KO cells, MCM-DH phosphorylation by DDK spreads to heterochromatin. As a result, TRESLIN-MTBP binds to phospho-MCM-DH and becomes diluted, leading to random initiation and the loss of IZ and RT.