[1] Imperial Canc Res Fund, POB 123, London WC2A 3PX, England
[2] Forschungsinst Mol Pathol, IMP, A-1090 Vienna, Austria
[3] Univ Vienna, Inst Algemeine Biochem, A-1090 Vienna, Austria
[4] Univ Vienna, Ludwig Boltzmann Forsch Stelle, A-1090 Vienna, Austria