[DNA-protein interactions in HeLa cells at different phases of the mitotic cycle and in the resting state].

The tight association between DNA and protein in chromatin is characteristic of HeLa cells in all stages of the cell cycle as revealed by nucleoprotein-celite-chromatography. The complex can be dissociated only by 4 M LiCl and 8 M urea at 90 degrees C (form II). The arrest in G1, S and mitosis did not induce any changes in DNA-protein interactions, chromatin remained in form II. Transition of the cells into quiescence induced by medium exhaustion or by serum deprivation was coupled with weakening of DNA-protein bonds. A significant part of DNA was released from the complex with protein by 1.5 M LiCl, 8 M urea at 2-4 degrees C (form I). Simultaneously with form I appearance the increase of DNA one-strand breaks was observed. The qualitative differences in the DNA-protein interactions of chromatin between cycling and quiescent cells evidence the existence of alternative to the cell cycle stage of cell quiescence--Go-phase.