a, Schematic of the DNA fibre assay that was used to measure fork protection by calculating IdU:CldU ratios. b, c, IdU:CldU ratios from U20S cells in which BRCA1 or PALB2 expression was knocked down by siRNA transfection and cells were treated with hydroxyurea (5 mM, 3 h). n = 300 fibres from 3 biological replicates; bars depict median ± 95% CI. c, Representative blot (n = 3). d, Schematic of BRCA1 protein, indicating RING (red), RAD51-binding (green), coiled-coil (blue) and BRCT repeat (purple) domains. The M1411T patient variant disrupts binding of PALB2 and is located in the coiled-coil domain. e, Schematic of PALB2 protein, indicating BRCA1-interacting coiled-coil (blue), ChAM and DNA-binding (purple and green) and WD40-like repeat (orange) domains. The PALB2(ΔNT) mutant lacks the N-terminal coiled-coil domain. f, Colony survival following cisplatin treatment (2.5 µM, 2 h) in HeLa cells in which BRCA1 expression was knocked down by siRNA transfection and cells were complemented with Flag–eGFP-tagged wild-type BRCA1 or Flag–eGFP-tagged BRCA1(M1411T). n = 4; data are mean ± s.e.m. g, Colony survival after cisplatin treatment (2 h) in U20S cells in which PALB2 expression was knocked down by siRNA transfection and cells were complemented with Flag-tagged wild-type PALB2 or Flag-tagged PALB2(ΔNT). n = 4; data are mean ± s.e.m. h, Representative blot for j (n = 3). i, Representative blot for k (n = 3). j, IdU:CldU ratios from U20S cells in which BRCA1 expression was knocked down by siRNA transfection, cells were complemented with Flag–eGFP-tagged wild-type BRCA1 or Flag–eGFP-tagged BRCA1(M1411T) and treated with hydroxyurea (5 mM, 3 h). n = 300 fibres from 3 biological replicates; bars depict median ± 95% CI. k, IdU:CldU ratios from U20S cells in which PALB2 expression was knocked down by siRNA transfection, cells were complemented with Flag-tagged wild-type PALB2 or Flag-tagged PALB2(ΔNT) and treated with hydroxyurea (5 mM, 3 h). n = 300 fibres from 3 biological replicates; bars depict median ± 95% CI. l, Percentage of stalled replication forks in U20S cells in which BRCA1 expression was knocked down by siRNA transfection and cells were complemented with Flag–eGFP-tagged wild-type BRCA1 or Flag–eGFP-tagged BRCA1(M1411T). n = 3; data are mean ± s.e.m. m, As for l but for knockdown of PALB2. Cells were complemented with Flag-tagged wild-type PALB2 (n = 3) or Flag-tagged PALB2(ΔNT) (n = 3). n = 2 for NTC and siPALB2; data are mean ± s.e.m. n, Percentage of replication forks that were able to restart after hydroxyurea treatment (5 mM, 3 h) in U20S cells in which BRCA1 expression was knocked down by siRNA transfection and cells were complemented with Flag–eGFP-tagged wild-type BRCA1 or Flag–eGFP-tagged BRCA1(M1411T). n = 3; data are mean ± s.e.m. o, As for n but for knockdown of PALB2. Cells were complemented with Flag-tagged wild-type PALB2 (n = 3) or Flag-tagged PALB2(ΔNT) (n = 3). n = 2 for NTC and siPALB2; data are mean ± s.e.m. A two-sided unpaired t-test was used to calculate all P values. Source Data