Nature 483, 295–301 (2012); doi:10.1038/nature10799

In Fig. 4a of this Article, the x-axis label “0” of the TBP panel for “No TSS” and “Dubious” should move to the left by one interval. In Fig. 4b and c, the x-axis labels of the TBP panel should read “−3, 0, +3”, not “−1, 0, +3”. These errors have been corrected in the original HTML and PDF versions online.