FIGURE 3.

A simplified example of the two models regulating transcription. (A) Linear distance of a regulatory element (RE) and a gene. (B) The addition of active or repressive histone marks will determine if the gene will be placed in an A or B compartment. (C) Looping model. Describes the classic model of activation of a gene upon looping. An enhancer is not in close proximity with its target gene and therefore it is not transcribed. Upon the binding of different TFs, looping of the enhancer to the target gene takes place and the gene is expressed. (D) Pre-looping model. The gene is in close proximity (looped) with the enhancer but not actively transcribed. However, recruitment of an additional (crucial) TF to the enhancer (depicted in a dark blue hexagon) initiates transcriptional activation of the promoter while preserving their close proximity. (E) The gene is in close proximity (looped) with the enhancer but not actively transcribed. The gene is placed in a (B) compartment, bound by the PCR complex.