Fig. 3
From: Decoding enhancer complexity with machine learning and high-throughput discovery
Current models of enhancer grammar. The flexibility of the type, number, orientation, and spacing of motifs within an enhancer sequence can vary (reviewed in [5, 78]). The enhanceosome model relies on fixed composition, number, and organization of motifs that support direct and cooperative binding of TFs [80], corresponding to enhancers with low sequence flexibility and thus increased sequence conservation. A greater degree of sequence flexibility is found in the billboard [79] and TF collective [76] enhancer models which incorporate variable motif organization and TF cooperativity