MRE11 binds poly(ADP-ribose). a, human cells were exposed for 1 h to 50 μm etoposide and then immunostained with anti-PAR polyclonal antibody 96-10 and anti-MRE11 monoclonal antibody. Colocalization of MRE11 foci with sites of PAR synthesis is shown. Images were collected as z-series, and only a single representative deconvolved plane is presented. Scale bars, 3 μm. The four bottom panels show three-dimensional renderings of MRE11, PAR, DNA (counter-stained with DAPI), and the colocalization channel. b, putative PAR-binding motif on MRE11 proteins. c, purified MRE11 binds specifically to automodified PARP1 and PAR in vitro, whereas MRE11 R/A mutant failed to bind both. First panel, Western blot of purified wild-type and mutant MRE11 proteins. d, MRE11 exonuclease assays were performed on a 32P-5′-end-labeled 63-bp double-stranded DNA substrate with the indicated amounts of MRE11 and PAR.
