CDKN2A and neoplasm: For instance, chromatin immunoprecipitation (ChIP; a method for determining sites of protein–DNA interactions in vivo) experiments show that silencing of the CDKN2A locus – which encodes the p16INK4A and p14ARF tumour suppressors – is associated with hypermethylation of H3K9 and hypomethylation of H3K4 (Nguyen et al, 2002).