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. 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.Comment: 6 pages, 4 figures, Supplemental Materia