Fig 1: RECQ4 C-terminal interaction with EMI1 is inversely correlated with RECQ4 N-terminal interaction with APC/C.a A schematic diagram of RECQ4 wild type (WT), Q757X mutant, C-terminal fragment (751–1028), and D1093X mutant. b Representative western blot analysis of the indicated proteins in whole-cell extracts (WCE) prepared from RECQ4 WT and D1093X expressing cells. Actin was used as a loading control. c Representative real-time cell growth assays to measure cell growth rate of HEK293 or RECQ4 knockdown (KD) cells with or without stable expression of FLAG-RECQ4 WT or D1093X mutant. n = 4 (biologically independent samples), except HEK293 control cells, where n = 3 (biological independent samples). Data are presented as mean values ± SD. d Structure of RECQ4427-1116 (5LST) drawn using RProtein Data Bank. The residues visible in the structure between T449 and A480 that are part of ABD2 and important for APC/C interaction are shown in green. Visible residues (D1093 to E1111) missing in the D1093X mutation involved in EMI1 interaction are shown in pink. e Representative western blot analysis of the indicated proteins co-purified with FLAG-RECQ4 WT, Q757X, or 751–1208 from RECQ4 KD HEK293 cells stably expressing RECQ4 WT or truncation mutants shown in (a). f Representative western blot analysis of the indicated proteins in chromatin-bound (CB) fractions prepared from RECQ4 WT and D1093X expressing cells. LAMIN A/C was used as a loading control. g Representative western blot analysis of the indicated proteins co-purified with FLAG-RECQ4 WT or D1093X proteins from CB fractions prepared from the cells shown in (f). Source data are provided as a Source data file. h Schematic diagram of the proposed role of RECQ4-APC/C interaction in replication initiation. See “Discussion” for details.