Correction to: Nature Reviews Molecular Cell Biology https://doi.org/10.1038/s41580-021-00341-1, published online 15 March 2021.

The sentence ‘H3K9me3 is generally mutually exclusive with H3K27me3 and therefore…’ originally began with ‘H3K27me3’ instead of ‘H3K9me3’. This mistake has now been corrected in the HTML and PDF versions of the article.