a) As described in Methods, individual reactions containing equimolar amounts of unmodified (lanes 1–3) or acetylated (lanes 4–6) FLAG-tagged WRN were incubated without or with biotin-tagged 2-stranded fork or 4-stranded replication fork substrate (2 pmol) as indicated and added to streptavidin-agarose beads to bind biotin-tagged DNA. After washing away unbound WRN, bound proteins were released, separated by SDS-PAGE, detected by Western blotting using anti-WRN antibody, and visualized using chemiluminescence. b) For experiments performed as in A, signal intensity for amounts of bound WRN in DNA-containing samples was quantified and normalized to signal intensity for unmodified WRN bound to the 2-stranded fork. Data are mean and standard deviation from 5 independent experiments