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Figure S4. Model for chromatin assembly at mammalian telomeres and subtelomeres. Both telomeric and subtelomeric chromatin is enriched in trimethylated H3K9, which is performed by the Suv39h HMTases (Garcia-Cao, M., R. O�Sullivan, A.H. Peters, T. Jenuwein, and M.A. Blasco. 2004. Nat. Genet. 36:94-99). In turn, this modification creates an affinity site for the HP1 family of proteins that are important for heterochromatin assembly. In addition, subtelomeric DNA domains are enriched in methylated CpG residues, which are maintained by the Dnmt1, Dnmt3a, and Dnmt3b DNA methyltransferases (Gonzalo, S., I. Jaco, M.F. Fraga, T. Chen, E. Li, M. Esteller, and M.A. Blasco. 2006. Nat. Cell Biol. 8:416-424). Both telomeres and subtelomeres are also enriched in trimethylated H4K20, which is dependent on the activity of the Suv4-20h HMTases (this study). The Suv4-20h enzymes are recruited to chromatin through their interaction with the HP1 proteins (Schotta, G., M. Lachner, K. Sarma, A. Ebert, R. Sengupta, G. Reuter, D. Reinberg, and T. Jenuwein. 2004. Genes Dev. 18:1251-1262). Abrogation of Suv39h or Suv4-20h HMTases lead to the loss of telomere length control, increased telomere recombination, and increased APB frequencies independently of DNA methylation (this study). In turn, loss of DNA methylation can lead to the loss of telomere length control, increased telomere recombination, and increased APB frequencies independently of histone methylation (Gonzalo, S., I. Jaco, M.F. Fraga, T. Chen, E. Li, M. Esteller, and M.A. Blasco. 2006. Nat. Cell Biol. 8:416-424).