Vol. 210, No. 5, May 2013. Pages 951–968.
The authors regret that in their original paper, the RNU6 loading control panels shown in Fig. 1 (E and F) were incorrect as a result of an error in figure presentation during the final production process. The conclusions of the experiments shown in these panels are not affected. The corrected figure appears below. The online HTML and PDF versions of this article have been corrected. The error only remains in the print version.