An endodeoxyribonuclease activity in nuclei from rat-ascites hepatoma

The DNA in nuclei from rat-ascites hepatoma (AH) was rather resistant to endogenous endonucleolytic attack (autodigestion), compared with that in nuclei from normal rat liver (RL). In contrast, by micrococcal nuclease, the DNA in AH nuclei was cleaved in the same manner as in RL nuclei. A 0.6 M NaCl extract was prepared from RL or AH nuclei and subjected to Sephadex G-100 filtration. The resulting-nuclease fraction was separated further into two nuclease fractions, I and II, by CM-Sephadex column chromatography. The activity ratio of II to I was 7.1 for the RL and 2.0 for the AH nuclei. Moreover, the activity of fraction II from the AH nuclei was rather low, compared with that from the RL nuclei. Regenerating-liver nuclei from the normal rat were also assayed in the same way. The results obtained were very similar to those from the AH nuclei. In addition, each of fractions, I and II, cleaved pBR322 DNA of superhelical form; in other words, each had endonucleolytic ability.