In 2D electrophoresis, the visible DNA-bound protein complex in EMSA was excised from a native PAGE gel (Figure S4A–S4C) and sequenced directly, which identified lupus autoantigen Ku70/80 (XRCC5/6), nucleolin (NCL) and HSP90AA1/AB1 as the major constituents of the DNA–protein band (Table S11). Here, XRCC6 is linked to systemic lupus erythematosus.