The birth-diffusion-death model of position effects. (A) Sketch of the model. Rate-limiting complexes for expression are released from DNA at assembly sites and diffuse on chromatin until they dissociate. At each step of the diffusion process, the complexes “jump” to another site on the genome with a probability that is proportional to the value of the Hi-C contact matrix. (B) Models with unstable complexes better fit the expression of the reporters. The best model corresponds to release sites at both promoters and terminators, but it is only marginally better than assuming that complexes are released at terminators only. The black curve represents the predictive power of a null model where assembly sites have a uniform distribution. The half-life is measured in number of “jumps.”
