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VOLUME 289 (2014) PAGES 34683–34698
PAGES 34687 and 34688:
Two figures contain minor errors. In panel A of Fig. 2, the terms spliced and unspliced are reversed. The chemical structure shown in panel A of Fig. 3 should include two additional methyl groups attached to the ring at the right hand side of the molecule. This structure is shown correctly in supplemental Table 2 (A9). These corrections do not affect the interpretation of the results or conclusions of this work.
