Retraction to: Nature https://doi.org/10.1038/nature12201, published online 26 May 2013.

The authors are retracting this Article to correct the scientific literature, owing to issues with figure presentation and underlying data. The authors cannot confirm the results in the affected figures and thus wish to retract the Article in its entirety. Both authors, Abderrahmane Kaidi and Stephen P. Jackson, agree with the Retraction.