Nat. Protoc. 10, 1697–1708 (2015); published online 8 October 2015; corrected after print 2 December 2015

In the version of this article initially published, the third author's last name was spelled incorrectly. The spelling was initially 'Zong' but should have been 'Zhong'. The error has been corrected in the HTML and PDF versions of the article.