ИСТИНА

Packing of DNA presents one of the most challenging questions in contemporary molecular biology. Being about 2 meters long when fully extended, DNA is compacted on a microscale level inside the cell's core in a specific fashion. Several striking features of this packing have already been established: absence of knots, easy unentanglement of chromosome parts during the transcription, presence of distinct territories, ability of distant parts along the genome to find each other in so-called promoter-enhancer reactions. These properties have led to an idea of fractal organization of genom. Chromatin dynamics suggests indispensable tools for investigation of DNA organization. While the experiments on locus tracking already allow for low enough times of observation in order to "feel" the correlations in internal structure of chromatin, all the theoretical microscopic approaches rely on the simple Rouse model for a polymer, that results in the Gaussian statistics of the chain at all times. This crucial simplification is related to the difficulties of analytical tractability imposed by the direct introduction of volume interaction and viscoelasticity to the Langevin equation. Here we report a microscopical pair-wise approach for the potential of a self-avoiding chain that, being plugged into the Langevin equation, reproduces the exponents, predicted by scaling, and allows for a simple analytical tractability. Also the chain's statistics turns out to be fractal as it should be for the crumpled globule state. Moreover, in order to take into account viscoelastic properties of the environment, the model may be straightforwardly enriched by introduction of fractional Gaussian noise and the general Langevin equation based on the model can be simply constructed. We show that the presence of viscoelastic media does not change the fractal dimension of the equilibrium polymer conformation, but just retards the relaxation in the system. The characteristic times of relaxation of the chain have been established along with concrete relaxation patterns. Eventually, we suggest a theoretical framework to distinguish between the topological interactions (fractal dimension) and the influence of media viscoelasticity (memory) in the experiments on DNA locus tracking with the chromosome surrounded by some protein environment. These two factors in their certain combinations have an impact on the exponents, relaxation times and laws in fractal systems and, particularly, in the fractal globule.