About the Authors
Institute of Molecular Life Sciences, University of Zurich, Zurich, Switzerland
The authors have declared that no competing interests exist.
The author(s) have made the following declarations about their contributions: Conceived and designed the experiments: AB. Performed the experiments: JZK PR. Analyzed the data: JZK AB. Contributed reagents/materials/analysis tools: SS. Wrote the paper: JZK AB.