1 Ludwig Institute for Cancer Research and Department of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, California, USA.
2 Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA.
3 Instituto Gulbenkian de Ciência, Rua da Quinta Grande 6, Oeiras, Portugal.
4 Laboratory of Genetics, The Salk Institute for Biological Studies, La Jolla, California, USA.
5 Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
6 Ludwig Institute for Cancer Research and Department of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, California, USA. dcleveland@ucsd.edu.