About the Authors
Department of Molecular and Cellular Biology, Centro Nacional de Biotecnología-CSIC, Cantoblanco, Madrid, Spain
The authors have declared that no competing interests exist.
Conceived and designed the experiments: IB DR JFR. Performed the experiments: IB AMM DR JFR. Analyzed the data: IB DR JFR. Contributed reagents/materials/analysis tools: DR JFR. Wrote the paper: JFR.