[Novel biophysical and biological aspects of mechanisms of effects of low doses of ionizing radiation (low LET) on eukaryotic cells].

Novel biophysical and biological aspects of eukaryotic cell response to low doses of low-LET radiation are considered in the present paper. The model of universal nuclear target in eukaryotic cells is proposed. The target is considered as a spherical volume homogeneously filled of DNA with adjacent water layer. Thickness of water layer equals to diffusion length of hydroxil radicals hitting DNA. Two subregions are proposed of the cellular membrane with different ability to respond to low doses of ionizing radiation. An original mechanism of repair of DNA double strand breaks (dsb) is described. This mechanism suggests directional conformational movement of separate locuses of homological chromosomes through narrow tube ("throat") between specialised nuclear regions. The fluxes of nuclear liquid induce a force which is responsible for highly elastic chromosome deformation and chromosome movement resulting in proximity of homological chromosomes in the throat. Close proximity is required for DNA dsb repair. All of DNA dsbs have to be repaired in low doses range owing to high genomic stability of eukaryotic cells. However, it has been hypothesized an existence of a small subpopulation of cells with unstable genome named as cells of evolutionary or/and ontogenetical reserve (ER or/and OR). Genomic instability is induced in these cells by epigenetic program. This program results in DNA damage mainly in chromosomal "hot spots". As a result new genetic variants are originated. The ability of cell population in vivo to eliminate or not eliminate Er/OR cells determinates individual sensitivity of organism and hence health consequences to low dose radiation exposure.