Regulation of replication timing and chromatin architecture by nuclear membrane tethering of Rif

Rif1 was originally discovered as a telomere binding factor in yeasts. In mammalian cells, Rif1 was shown not to play major roles in telomere regulation, but to regulate DSB repair and replication stress response. Rif1 was shown to facilitate NHEJ during G1 phase and to play roles in protection of stalled replication fork and in elimination of chromosome entanglements during mitosis.

Now it is well established that Rif1 plays a major role in regulation of replication timing (RT). In this seminar, I would like first to describe how we identified Rif1 as a key regulator of RT in fission yeast, which led to recognition of a conserved role of Rif1 as a RT regulator in wide varieties of species. We also showed that Rif1 is a G4 (G-quadruplex) binding protein, and that G4 recognition plays a crucial role in RT regulation at least in fission yeast.

A portion of mammalian Rif1 is localized near nuclear periphery and is biochemically fractionated into detergent-resistant membrane fractions. Tagging of endogenous Rif1 with mSG (monomeric StayGold) fluorescent protein revealed that Rif1 associates with nuclear membrane during early/ mid S phase, and dissociates at mid/ late S phase to G2.

I would like to discuss our recent findings on how mammalian Rif1 is tethered to nuclear membrane, its role in RT regulation and compartment regulation. We particularly focus on the functions associated with the C-terminal segment (CTD) and a long IDP (intrinsically disordered polypeptides) connecting the N-terminal HEAT/Armadillo repeat sequences and CTD.