Reversible cross-linking of
proteins in nuclei and
DNA-depleted nuclei from Friend
erythroleukemia cells was used as a probe to determine whether the
protein structure was preserved following treatment with
DNAase 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, however, 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
DNAase I. However, 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.