Induction of DNA ligase during stimulation of DNA synthesis in intact rat liver by a dietary manipulation

Enhanced phosphorylation of a nucleolar 110-kDa protein in rat liver by dietary manipulation

RNA polymerase 1 activity and nucleolar volume have been reported to increase in hepatocytes from rats fed a protein-free diet. Phosphorylation in vitro of a 110-kDa protein was enhanced in nuclei and nucleoli from livers of rats fed a protein-free diet. In nuclear extracts the 110-kDa protein in heat-treated nuclei was much more phosphorylated than from control liver. In contrast, casein kinase activity in the nuclear extract from control liver was comparable to that from livers of rats fed a protein-free diet. Nuclear extracts from control rat liver and livers of rats fed a protein-free diet were fractionated by DEAE-cellulose column chromatography. Casein kinase II (NII) eluted at around 0.17 M NaCl scarcely phosphorylates the 110-kDa protein. Chromatography of the nuclear extract from livers of rats fed a protein-free diet, but not from control liver, yielded fractions which eluted at 0.21-0.25 M NaCl and predominantly phosphorylated the 110-kDa protein. The phosphorylation of 110-kDa protein was not appreciably affected by a heparin concentration of 5 micrograms/ml, which completely inhibited casein kinase II. In addition, phosphorylation of the 110-kDa protein in liver nucleoli from rats fed a protein-free diet showed a lower sensitivity to heparin than that in control rat liver nucleoli. These results suggest that enhanced phosphorylation of the nuclear 110-kDa protein in livers from rats fed a protein-free diet is due to the induction of a 110-kDa protein kinase distinct from casein kinase II.

Detection in situ of active polypeptides of mammalian and T4 DNA kinases after sodium dodecyl sulfate/polyacrylamide gel electrophoresis

DNA kinase activity of rat liver nuclei was detected in situ after electrophoresis in sodium dodecyl sulfate/polyacrylamide gel containing 5'-hydroxyl nicked DNA as DNA substrate. After renaturation of polypeptides, the gel was incubated with [gamma-32P]ATP and Mg2+. An active polypeptide corresponding to Mr 61,000 was observed as a radioactive band by autoradiography. The intensity of the band was proportional to the amount of the enzyme applied. The active band common to various tissues of rat was observed with the nuclear extracts, indicating that DNA kinase for rat tissue is composed of a single polypeptide of Mr 61,000. In contrast, T4 polynucleotide kinase (Mr = 140,000) showed an active polypeptide band corresponding to the subunit of Mr 33,000.

Immunochemical analysis of molecular forms of mammalian DNA ligases I and II

Using specific antibodies against calf thymus DNA ligases I and II (EC 6.5.1.1), we have investigated the polypeptide structures of DNA ligases I and II present in the impure enzyme preparations, and estimated the polypeptides of DNA ligases I and II present in vivo. Immunoblot analysis of DNA ligase I after sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a 130-kDa polypeptide as a major one in the enzyme preparations from calf thymus throughout the purification. In addition to the 130-kDa polypeptide, a 200-kDa polypeptide was detected in the enzyme preparations at the earlier steps of the purification, and a 90-kDa polypeptide was observed as a minor one in the enzyme preparations at the later steps of the purification. The polypeptides with molecular weight of 130 000 and 90 000 were detected by SDS-polyacrylamide gel electrophoresis of DNA ligase I-[3H]AMP complex. These results suggest that a 200-kDa polypeptide of DNA ligase I present in vivo is degraded to a 130-kDa polypeptide and then to a 90-kDa polypeptide during the isolation and purification procedures. On the other hand, the monospecific antibody against calf thymus DNA ligase II cross-reacted with only a 68 kDa polypeptide in the enzyme preparations throughout the purification, suggesting that the 68-kDa polypeptide is a single form of calf thymus DNA ligase II present in vivo as well as in vitro.