[1] Harvard Univ, Sch Engn & Appl Sci, Dept Phys, Engn & Sci Lab, Cambridge, MA 02138 USA
[2] Harvard Univ, Sch Med, Brigham & Womens Hosp, Boston, MA USA
[3] German Canc Res Ctr, Div Mol Genet, Heidelberg, Germany
[4] Univ Basel, Biozentrum, Maurice E Muller Inst Struct Biol, Basel, Switzerland