CROSS-LINKING OF PROTEINS IN NUCLEI AND DNA-DEPLETED NUCLEI FROM FRIEND-ERYTHROLEUKEMIA CELLS

Reversible cross-linking of proteins in nuclei and DNA-depleted nuclei from [murine] Friend erythroleukemia cells was used as a probe to determine whether the protein structure was preserved following treatment with DNase I. Interactions between histones were analyzed through cross-linking with 2-iminothiolane or dimethyl 3,3''-dithiobispropionimidate. No alterations in the interactions between intranucleosomal histone proteins resulted from digestion of the nuclear DNA. There was a diminished extent of cross-linking of histone H1 to itself and to the intranucleosomal histones in DNA-depleted nuclei. The interactions of a group of nonhistone proteins with histone H3 could be monitored by cross-linking through the formation of disulfide bonds caused by oxidation of nuclei with H2O2. These interactions were not markedly affected by treatment of the nuclei with DNase I. Differences were observed in the extent of cross-linking of some of these proteins when cross-linking in nuclei from undifferentiated cells was compared to that in nuclei from cells which had been induced to differentiate with dimethylsulfoxide.