Replicative DNA synthesis and unscheduled DNA synthesis in permeable sarcoma cells studied by nuclease digestion

About 20% of DNA replicated in vitro in permeable mouse ascites sarcoma cells showed higher sensitivity to staphylococcal nuclease than the sensitivity of bulk DNA, and the remaining part showed the same nuclease sensitivity as that of parental chromatin DNA. The sensitivity of DNA replicated in permeable cells was higher than that of DNA newly replicated in vivo in intact cells, and close to that of DNA newly replicated in vivo in the presence of cycloheximide. Bleomycin-induced unscheduled DNA synthesis in permeable cells was highly sensitive to the nuclease. The results suggest that DNA replicated in vitro and parental nuclear protein form immature nucleosomes, probably in the same way as in vivo chromatin replication in the presence of protein synthesis inhibitors. It also appears that bleomycin-induced, unscheduled DNA synthesis occurs largely in the internucleosomal region.