Fig. 8: RIF1-L interacts with BRCA1 to promote RAD51-dependent homology repair of broken forks.

A Model of how RIF1-L promotes recovery from replication stress. (i) Replication fork progresses in unperturbed condition. (ii) Replication fork stalls upon replication stress. RIF1 and BRCA1 are independently recruited to stalled forks. (iii) Persistent stalling leads to fork breakage and subsequent formation of a single-ended DSB. RIF1-L interacts with BRCA1 dependent on phosphorylation of RIF-L S²²⁶⁵. RAD51 localises to broken forks. (iv) RIF1-L-BRCA1 complex facilitates the loading of RAD51 onto seDSBs. RAD51 nucleofilament thereby initiate strand invasion into the sister chromatid and proceed to homology-directed repair. B A speculative model proposing that RIF1-L may bridge the broken daughter and parental DNAs. Unmethylated H4K20 is enriched on newly-replicated nascent chromatin (pale orange octagons), enabling BRCA1-BARD1 recruitment. Di-methylated H4K20 is enriched on un-replicated parental chromatin (grey octagons), favouring 53BP1. We speculate that RIF1-L may bind BRCA1 via its C-terminal phosphorylated SPKF motif, while interacting with 53BP1 via its N-terminal residues. In this manner, RIF1-L may facilitate the homology pairing between sister chromatids. In the RIF1-L protein, pale blue curve represents the IDR region; red bar represents the S²²⁶⁵PKF motif. ‘N’ and ‘C’ marks N-terminal and C-terminal of the RIF1-L protein.