  We investigated the viscoelastic response of model interphase chromosomes by
tracking the three-dimensional motion of hundreds of dispersed Brownian
particles of sizes ranging from the thickness of the chromatin fiber up to
slightly above the mesh size of the chromatin solution. In agreement with
previous computational studies on polymer solutions and melts, we found that
the large-time behaviour of diffusion coefficient and the experienced viscosity
of moving particles as functions of particle size deviate from the traditional
Stokes-Einstein relation, and agree with a recent scaling theory of diffusion
of non-sticky particles in polymer solutions. Interestingly, we found that at
short times large particles are temporary "caged" by chromatin spatial
constraints, which thus form effective domains whose size match remarkably well
recent experimental results for micro-tracers inside interphase nuclei.
Finally, by employing a known mathematical relation between the time
mean-square displacement of tracked particles and the complex shear modulus of
the surrounding solution, we calculated the elastic and viscous moduli of
interphase chromosomes.
