Nature Communications 3: Article number: 1297 (2012); Published: 18 December 2012; Updated: 26 February 2013.

The original version of this Article contained a typographical error in the spelling of the author Hyung-Gon Mang, which was incorrectly given as Hyong-Gon Mang. This has now been corrected in both the PDF and HTML versions of the Article.