DIVERSITY OF NUCLEAR-PROTEIN FRACTIONS OF HAMSTER LIVER AND HEPATOMA PRODUCED BY DNASEI

The structural and functional diversity between active and inactive ch romatin is thought to depend, in part, upon differences in DNA-bound p rotein composition, including changes in the number of sulfhydryl grou ps. The aim of the present study was to compare protein composition in untreated nuclei, DNaseI-released and resistant nuclear fractions of hamster liver and Kirkman-Robbins hepatoma cells. Electrophoretic anal ysis of nuclear proteins showed some evident quantitative and qualitat ive differences between normal and neoplastic cells. The most signific ant diversities were noticed in DNaseI solubilized fraction of both ty pes of cells. Nuclease attack released a characteristic set of non-his tones with mel. wt 37,000, 50,000, 74,000 and 130,000-160,000 from tra nsformed cells, and polypeptides of mel. wt 45,000 and 76,000 from nor mal cells. Cell-specific distribution within examined nuclear polypept ides was revealed using selective staining of their protein-bound sulf hydryls, Immunoblot analysis demonstrated that a non-histone protein w ith mel. wt 48,000, overexpressed in rodent tumour cells, was exclusiv ely concentrated in liver DNaseI-sensitive fraction, which amounted on ly to 8.3% +/- 2.0% of total nuclear DNA. In hepatoma cells, however, this particular polypeptide is distributed between nuclease-sensitive and nuclease-resistant nuclear fractions. Non-histone protein of mel. wt 48,000 appeared to contain free sulfhydryl groups. In summary, thes e results show molecular specificity of nuclear proteins from normal a nd tumour cells and differences in their distribution among nuclease-r eleased and nuclease-resistant nuclear fractions. The diversity in mol ecular characteristics and sulfhydryl group patterns observed among th e examined proteins of normal and neoplastic cells may suggest their i nvolvement in some changes in the rearrangement of nuclei during neopl astic transformation.