Schematic representation of constitutive heterochromatin formation in mammals. SUV39H is the responsible HTMase for H3K9me3 on pericentromeres, a histone mark recognized by HP1 proteins. HP1 proteins interact and recruit SUV420H and DNMTs, leading to H4K20me3 and DNA methylation, respectively. These epigenetic marks function also as docking sites, like H4K20me3 for ORC (origin of replication complex) proteins and CpGme for MBDs (factors with a methyl-binding domain). An alternative for DNMT recruitment might be through UHRF1 that directly interacts with DNMT1 and might read the H3K9me3 mark. In general, proteins involved in various pathways are required for heterochromatin formation and maintenance, and are listed in this panel.