Establishment of sister chromatid cohesion is coupled to DNA replication, but the underlying molecular mechanisms are incompletely understood. DDX11 (also named ChlR1) is a super-family 2 Fe-S cluster-containing DNA helicase implicated in Warsaw breakage syndrome (WABS). Herein, we examined the role of DDX11 in cohesion establishment in human cells. We demonstrated that DDX11 interacts with Timeless, a component of the replication fork-protection complex, through a conserved peptide motif. The DDX11-Timeless interaction is critical for sister chromatid cohesion in interphase and mitosis. Immunofluorescence studies further revealed that cohesin association with chromatin requires DDX11. Finally, we demonstrated that DDX11 localises at nascent DNA by SIRF analysis. Moreover, we found that DDX11 promotes cohesin binding to the DNA replication forks in concert with Timeless and that recombinant purified cohesin interacts with DDX11 in vitro. Collectively, our results establish a critical role for the DDX11-Timeless interaction in coordinating DNA replication with sister chromatid cohesion, and have important implications for understanding the molecular basis of WABS.

Warsaw breakage syndrome (WABS), is caused by biallelic mutations of DDX11, a gene coding a DNA helicase. We have recently reported two affected sisters, compound heterozygous for a missense (p.Leu836Pro) and a frameshift (p.Lys303Glufs*22) variant. By investigating the pathogenic mechanism, we demonstrate the inability of the DDX11 p.Leu836Pro mutant to unwind forked DNA substrates, while retaining DNA binding activity. We observed the accumulation of patient‐derived cells at the G2/M phase and increased chromosomal fragmentation after mitomycin C treatment. The phenotype partially overlaps with features of the Fanconi anemia cells, which shows not only genomic instability but also defective mitochondria. This prompted us to examine mitochondrial functionality in WABS cells and revealed an altered aerobic metabolism. This opens the door to the further elucidation of the molecular and cellular basis of an impaired mitochondrial phenotype and sheds light on this fundamental process in cell physiology and the pathogenesis of these diseases.

FANCJ is a DNA helicase linked to Fanconi anemia and frequently mutated in breast and ovarian cancers. If and how FANCJ is recruited to the replisome is unknown. Here, we report that FANCJ directly binds to AND-1 (the vertebrate ortholog of budding yeast Ctf4), a homo-trimeric protein adaptor that connects the CDC45/MCM2-7/GINS replicative DNA helicase with DNA polymerase α and several factors at DNA replication forks. We find that the interaction between FANCJ and AND-1 requires the integrity of an evolutionarily conserved Ctf4-interacting protein (CIP) box located between the FANCJ helicase motifs IV and V. Disruption of the FANCJ CIP box significantly reduces FANCJ association with the replisome, causing enhanced DNA damage, decreased replication fork recovery and fork asymmetry in stressful conditions. Cancer-relevant FANCJ CIP box variants display reduced AND-1-binding, a finding that suggests a potential role of the mutatedFANCJalleles in cancer predisposition.