Nucleosomal DNA isolated from bleomycin-treated nuclei shows retarded electrophoretic mobility in neutral gels as compared with the sample isolated from micrococcal (or endogenous) nuclease-digested nuclei. The retardation in electrophoretic mobility is probably due to the presence of single-strand regions in the DNA duplex of bleomycin-treated samples as determined by single-strand-specific S1 nuclease digestion and buoyant density measurements. This observation argues against the possibility that the generation of nucleosomal DNA following drug treatment of nuclei is due to an activation of endogenous nuclease by bleomycin and strongly suggests that the drug has a unique feature of action on chromatin.


Supported by Research Grant CD-25 awarded by the American Cancer Society, Inc.

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