筒井 研

DNA damage induced by cis-diamminedichloroplatinum (II) (cisplatin: cis-DDP), an anticancer drug, was studied in vitro by monitoring the drug-induced conformational change of pUC18 plasmid DNA, the sensitivity to some restriction enzymes of the damaged DNA and the sequence-dependent termination of DNA synthesis caused by cisplatin. Closed circular, superhelical pUC18 DNA was treated at 37 degrees C for 16 h with various concentrations of cisplatin. Cisplatin-dose-dependent conformational change due to unwinding of the treated DNA was detected by agarose gel electrophoresis. To analyze the base-specificity of the cisplatin damage, the measurement for sensitivity of cisplatin-treated DNA to various types of restriction enzyme and sequence gel analysis of the treated DNA were conducted. The results suggested that cisplatin attacked preferentially the sequence of GG > AG > GNG in the order. In the present assay condition, the cisplatin/DNA nucleotide ratios required for the DNA damage detection were roughly 0.025 for the conformational analysis, 0.001 or more for the restriction enzyme analysis, and less than 0.001 for the sequence gel analysis. By using the present method, it was demonstrated that the cisplatin-mediated DNA damage was inhibited by NaCl, KCl, CaCl2 or MgCl2 at their nearly physiological concentrations, and by reducing agents such as thiourea and 2-mercaptoethanol in the reaction mixture.

The susceptibility of Rous sarcoma virus (RSV) genomes integrated in mouse ascites sarcoma cells (SR-C3H/He cells) to DNase I and DNase II was investigated. Approximately half of the viral sequences were sensitive to DNase I and DNase II when 17% and 7.4% of the chromatin DNA was rendered acid soluble, respectively. The results suggest that newly acquired exogenous proviral sequences are integrated into both transcriptionally active and inactive regions of chromatin in cells lacking related endogenous viral sequences.

DNA repair synthesis induced in permeable mouse ascites sarcoma cells by peplomycin, an antitumor antibiotic, was studied. Mouse ascites sarcoma (SR-C3H/He) cells were permeabilized with a low concentration of Triton X-100 in an isotonic condition. Permeable cells were treated with an appropriate concentration of peplomycin to introduce single-strand breaks in permeable cell DNA. DNA repair synthesis in peplomycin-treated permeable cells was measured by incubating the cells with four deoxynucleoside triphosphates in an appropriate buffer system. The DNA repair synthesis was enhanced by ATP and NaCl at near physiological concentrations. More than 90% of DNA synthesis in the present system depended on the peplomycin-treatment. The repair nature of the DNA synthesis was confirmed by a BrdUMP density shift technique. The repair patches were largely completed and ligated in the presence of ATP. Analyses using selective inhibitors for DNA polymerases showed that both DNA polymerase Beta and aphidicolin-sensitive DNA polymerases (DNA polymerase alpha and/or delta) were involved in the repair DNA synthesis.</P>

Catalase was partially purified (about 380-fold purification) from the post-mitochondrial supernatant of bovine heart and compared with catalases from bovine erythrocytes and bovine liver. The electrophoretic mobility in polyacrylamide gel (pH 8.0) of heart catalase was the same as that of erythrocyte catalase and was smaller than that of the liver enzyme. The heart catalase was indistinguishable from erythrocyte catalase in regard to the molecular weights of subunit polypeptides, the inhibition patterns produced by several catalase inhibitors, and specific activity. The pH-activity curve of heart catalase consisted of a characteristic biphasic pattern with a peak at pH 7.5 and a shoulder at pH 10.

The nuclear matrix is an operationally defined nuclear skeletal structure that is believed to be involved in many nuclear functions including DNA replication, transcription, repair, and prem RNA processing/transport. Until relatively recently, the nuclear matrix was thought to be a rigid and static structure, but it is now thought to be dynamic. This paradigm shift was based in part on the tracking of the intranuclear movement of proteins tagged with fluorochromes. In this review, we attempt to redefine the nuclear matrix in light of recent findings and describe some useful techniques for the dynamic analysis of nuclear function.

Genomic sequencing and chromosomal assignment of the gene encoding rat APEX nuclease, a multifunctional DNA repair enzyme, were performed. An active Apex gene and a processed pseudogene were isolated from a rat genomic library. The active Apex gene consists of 5 exons and 4 introns spanning 2.1 kb. The putative promoter region of the Apex gene lacks the typical TATA box, but contains CAAT boxes and a CpG island having putative binding sites for several transcription factors, such as Sp1, AP-2, GATA-1 and ATF. A putative O-sialoglycoprotease (a homologue of Pasteurella haemolytica glycoprotease, gcp; abbreviated as Prsmg1/Gcpl1) gene consisting of 11 exons and 10 introns spanning 7.3 kb lies immediately adjacent to the Apex gene in a 5'-to-5' orientation. The Apex gene locus was mapped to rat chromosome 15p12 using in situ hybridization. The processed pseudogene (designated as rat Apexp1) has a nucleotide sequence 87.1% identical to that of the rat Apex cDNA, although several stop codons interrupting the coding sequences and multiple nucleotide deletions were observed. The Apexp1 is located in an inactive LINE sequence. Calculation of nucleotide substitution rates suggests that the immediate, active progenitor of Apexp1 arose 23 million years ago and that the non-functionalization occurred 15 million years ago.

The extent of homology between two protein fractions was compared by simple electrophoretic analysis. Nuclear proteins of several rodent cells of different origins were fractionated into acid-soluble and acid-insoluble fractions. The two protein fractions were subjected to polyacrylamide gel electrophoresis in separate gel systems, and protein bands with identical mobilities were sought either in all possible combinational pairs of cell types or in all cell types. The paired and overall homology indices calculated from these data and chi-square testing of the results indicated that acid-soluble nuclear nonhistone proteins are more homologous than acid-insoluble nuclear proteins. Several factors which might have affected the results were discussed.

Phosphate-binding protein(s) was found in the inner mitochondrial membrane of calf heart by Sephadex G-200 and G-25 gel filtration. The binding activity was inhibited by N-ethylmaleimide and competed by a large amount of cold phosphate. The amount of phosphate bound to the fraction was 29 nmoles per mg of protein. Affinity chromatography with phosphate-bound Sepharose 4B confirmed the presence of phosphate-binding protein(s) in the active fraction of mitochondrial membrane fractionated by gel filtration.

Preparations of IgG2b purified from several mouse hybridoma clones were highly susceptible, compared to other subclasses, to peptic digestion under conditions usually used to prepare F (ab')2 fragments. Analyses of the digestion products revealed that no F (ab')2 was produced and that the main product was a Fab-like fragment. Demonstration of the hinge disulfides in the Fc portion clearly indicated that in IgG2b the primary peptic cleavage occurs on the NH2-terminal side of the inter-heavy chain disulfide bridge. The resulting Fab failed to bind with antigen, suggesting the importance of the CH1-hinge region in maintaining the native conformation of the antigen-binding site.

The major gag protein (p34) of squirrel monkey retrovirus-H was purified in one chromatographic step by anion-exchange high performance liquid chromatography. The virus in a crude fraction was disrupted with Brij 35 in the presence of three kinds of protease inhibitors. The soluble virus lysate was injected into a Polyanion SI column, and p34 was eluted with a linear salt gradient. The recovery of the protein was about 60%. The purified p34 was nearly homogenous as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and silver staining.

The precipitation reaction of bovine serum albumin coupled with p-azophenylleucine with homologous antibody was inhibited by several structurally related haptens. The isobutyl group substituent on alpha-carbon atom of the leucine residue contributed more than -5.8 Kcal/mol to the free energy of binding. This value was consistent with the free energy change expected from the transfer of n-butane from an aqueous environment to liquid n-butane. The observed contribution was explained, in terms of the hydrophobic interaction of the isobutyl group with the antigen binding site of the antibody molecule. These results were also compared with other hapten-antibody systems.

We purified a 44-kDa nuclear protein from salt-extract of permeable mouse ascites sarcoma cells in an effort to isolate factors involved in the repair of acid-depurinated DNA. It was copurified with a major AP endonuclease (APEX nuclease) by sequential column chromatography then further purified by sodium dodecyl sulphate-poly-acrylamide gel electrophoresis as a possible DNA repair support factor. Its partial amino acid sequences were determined, and a cDNA clone for the protein was isolated from a mouse T-cell cDNA library using long degenerate oligonucleotide probes deduced from the amino acid sequence. The complete nucleotide sequence of the cDNA (1.7 kilobases) was determined. Northern hybridization using this cDNA detected two transcripts: 1.8kb being the major one and 2.6 kb being the minor one. The complete amino acid sequence for the protein predicted from the nucleotide sequence of the cDNA indicates that the 44-kDa protein consists of 394 amino acids with a calculated molecular weight of 43,698. In tests performed thus far, the recombinant 44-kDa protein expressed in Escherichia coli has not expressed any repair-support activity. It remains to be analyzed whether the protein attains this activity after appropriate posttranslational modifications. Most parts of the 44-kDa protein cDNA and the deduced amino acid sequence were found to be identical to those of the protein p38 -2G4, recently reported as a cell cycle-specifically modulated nuclear protein of 38kDa. The p38-2G4 may be a truncated form of the present 44-kDa protein.

Simian virus 40 (SV40) large T antigen was partially purified from small amounts of SV40-infected and SV40-transformed cells by immunoaffinity chromatography with high recovery. T antigen, in both crude and partially purified states, was detected rapidly by a sensitive and quantitative enzyme-linked immunosorbent assay (ELISA). Stability of the partially purified T antigen was found to increase by addition of 0.01% bovine serum albumin (BSA).