Chromatin compartments from correlated active processes

Gene transcription and its regulation involve active, energy-consuming processes, which induce correlated motion and enhance the subdiffusion of chromosomal loci. However, our current understanding of chromatin folding is largely based on equilibrium theories. To address this gap, we study a model of an active polymer driven by correlated active forces with non-uniform magnitude. Our analysis shows that active regions of the polymer bend and expand, while inactive regions straighten out and condense, resembling the morphology of heterochromatin (B) and euchromatin (A). Using polymer simulations, we predict that modest activity differences are sufficient to recapitulate the degree of AB compartmentalization observed in chromosome conformation capture (3C) experiments. Moreover, we find that distinct loci experiencing correlated active forces will effectively attract as if coupled by harmonic springs, while anticorrelations lead to repulsion. Thus, our theory offers non-equilibrium mechanisms for forming genomic compartments, which cannot be distinguished from affinity-based folding using structural data alone. Collectively, our work provides new avenues for the interpretation of data on chromosomes, and has broad implications for active polymer systems.