EFFECT OF UV-IRRADIATION OF RAT-LIVER NUCLEI ON STRUCTURAL TRANSITIONS AND FRACTIONATION OF THE CHROMATIN

The effect of UV-irradiation on the chromatin fractionation from DNase I-treated rat liver nuclei by solutions with different concentration of magnesium cations and ionic strengths has been investigated. Compar ative analysis of the biochemical parameters of five fractions isolate d from irradiated and non-irradiated nuclei has shown marked changes i n the amounts of DNA, RNA, and proteins and in the protein composition . UV-Irradiation induces the dose-dependent transition of some chromat in from the S3 and S4 fractions into the insoluble P4 fraction. Chroma tin content in fractions soluble in media with high concentrations of magnesium ions (S1 and S2.) does not change on irradiation. Decrease i n extraction of many proteins after UV-irradiation of both nuclei and preliminarily isolated fractions of the chromatin was observed. Change s in protein content and protein electrophoresis patterns of the fract ions as a consequence of exposure of the nuclei to UV-light may be the result of DNA-protein cross-linkage. A profound effect of UV-irradiat ion on stabilization of chromatin macrostructure in its condensed regi ons was observed.