Transcription-Induced Active Forces Suppress Chromatin Motion by Inducing a Transient Disorder-To-Order Transition

 Recent experiments have shown that the mobility of human interphase chromosome decreases during transcription, and increases upon inhibiting transcription, a finding that is counter-intuitive because it is thought that the active mechanical force (F) generated by RNA polymerase II (RNAPII) on chromatin would render it more open and mobile. Inspired by these observations, we use a copolymer model to investigate how F affects the dynamical properties of a single chromatin. The movements of the loci in the gene-rich region are suppressed in an intermediate range of F, and are enhanced at small and large F values. In the intermediate F, the bond length between consecutive loci increases, becoming commensurate with the location of the minimum in the attractive interaction between the active loci. This results in a transient disorder-to-order transition, leading to the decreased mobility during transcription. Our study suggests that transient ordering of the loci in the gene-rich region might be a mechanism for nucleating a dynamic network involving transcription factors, RNAPII, and chromatin.