Alternative models for the formation of epigenetic domains in complex genomes. In a sequence-independent model (left), histone-modifying enzymes respond to local signals, but subsequent establishment and maintenance of epigenetic modifications within larger domains are largely independent of the overall sequence composition of that domain. The extent of the domain, however, might be determined by other local sequence-specific features such as boundary elements. In a sequence-dependent model (right), recruitment and spreading of histone-modifying enzymes is guided by features of the primary genomic sequence throughout the domain, with different sequence features specifying or influencing different modifications across domains genome-wide.
Wang and Willard BMC Genomics 2012 13:367 doi:10.1186/1471-2164-13-367