© The Author(s) (published by Nature Publishing Group and the European Molecular Biology Organization) Posted on May 23, 2013 by SCG DR Copyright Holders: © The Author(s) (published by Nature Publishing Group and the European Molecular Biology Organization) Self-archiving policy Conditions Accepted version: √ Open Access Journal Published version: √ Open Access Journal Remarks: All articles in NPG’s open -access journal Molecular Systems Biology are published under a Creative Commons attribution-non commercial-share alike unported licence or a non commercial-no derivs licence, at the choice of the authors. Verification Date: 23.05.2013