Nature 453, 948–951 (2008); doi: 10.1038/nature06947

In this Letter, Fig. 4g and Supplementary Fig. 5f depict an analysis of H3K9me3 (not H3K9me2) ChIP data. In addition, three sentences in the third paragraph of the ‘Microarray data analysis’ section of the Methods should read: “Gene expression data and H3K27me3 ChIP data are from Tig3 lung fibroblasts18. H3K9me3 ChIP data are from human fetal lung fibroblasts30… H3K4me2 and PolII ChIP data are from WI38 human lung fibroblasts29.”.