Set9 is a histone methyltransferase which specifically methylates lysine 4 of histone H3 being a specific tag for epigenetic transcriptional activation. Further, methylation of histone H3K4 by Set9 precludes deacetylation of H3 by the NuRD complex and impairs Suv39h1-mediated methylation of H3K9. Set9 also methylates the tumor suppressor p53 at lysine 372, thereby enhancing its stability. It contains a SET domain but lacks the pre- and post-SET domains).