The N-terminal tail controls binding to both DNA and histones. (A) Amino acid sequence of the human RCC1 N-terminal tail. (B) Deletion of the tail significantly decreases chromatin binding. MDCK cells plated on a poly-lysine–coated coverglass were permeabilized, and identical concentrations of recombinant proteins RCC1-YFP and RCC1(Δ1–20)-YFP were added. Images were collected before and after the cells were washed sequentially with buffers containing indicated NaCl concentrations. (C) Deletion of the tail abolishes DNA binding. Recombinant RCC1-His₆ or RCC1(Δ1–20)-His₆ proteins were incubated with DNA-agarose beads or plain agarose beads. Bound proteins were detected by Coomassie blue staining. The gels were scanned and quantified by densitometry (left). The right panel shows representative DNA binding. (D) α-N-amino methylation of RCC1 further promotes RCC1 binding to DNA. Recombinant RCC1(Δ1–20)-His₆, WT RCC1-His₆, or purified Me-RCC1-His₆, which had been methylated in vitro, was incubated with agarose beads as in B. Proteins were detected and quantified by immunoblotting with anti-His6 antibody and an Odyssey scanner. (E) The RCC1 tail negatively regulates histone binding. Recombinant RCC1-His₆ or RCC1(Δ1–20)-His₆ was incubated at various concentrations with biotin-labeled core histones on streptavidin beads or with streptavidin beads alone. Bound proteins were detected by ECL with anti-His6 antibody (right) and quantified (left) as in B. Error bars represent ±1 SD.