Chromosomal Loci Move Subdiffusively Through a Viscoelastic Cytoplasm

Abstract

Tracking of fluorescently labeled chromosomal loci in live bacterial cells reveals a robust scaling of the mean square displacement (MSD) as τ0.39. We use Brownian dynamics simulations to show that this anomalous behavior cannot be fully accounted for by the classic Rouse or reptation models for polymer dynamics. Instead, the motion seems to arise from the interaction of the Rouse modes of the DNA polymer with the viscoelastic environment of the cytoplasm. To demonstrate these physical effects, we present a general analytical derivation of the subdiffusive scaling for a monomer in a polymer within a viscoelastic medium. The time-averaged and ensemble-averaged MSD of chromosomal loci exhibit ergodicity, and the velocity autocorrelation function is negative at short time lags. These observations are most consistent with fractional Brownian motion and rule out a continuous time random walk model.