Vol. 199 No. 3, October 22, 2012. Pages 481–496.

The authors recently discovered inadvertent duplication of figure panels in Figs. 4 A and S4 A. These duplications occurred during the process of figure compilation. The authors provided the journal with the correct original representative data and replicates. These data confirm that correcting these duplications does not impact the interpretation of the figure or the conclusions of the paper. The authors apologize for the error.

The HTML and PDF versions of the article have been corrected. The error remains only in the print version.