[1] Royal Free & Univ Coll Med Sch, Sch Med, Ludwig Inst Canc Res, London W1W 7BS, England
[2] Univ London Birkbeck Coll, Sch Crystallog, London WC1E 7HX, England
[3] Kings Coll London, Randall Div Cell & Mol Biophys, London SE1 1UL, England
[4] UCL, Dept Biochem & Mol Biol, London WC1E 6BT, England
[5] Kings Coll London, Div Canc, London SE1 1UL, England