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L M Chang

Publications and source records attributed to L M Chang.

At least 37 records · Page 2Linked to original sources
PubMed1984

DNA polymerase I and DNA primase complex in yeast.

Chromatographic analysis of poly(dT) replication activity in fresh yeast extracts showed that the activities required co-fractionate with the yeast DNA polymerase I. Since poly(dT) replication requires both a primase and a DNA polymerase, the results of the fractionation studies suggest that these two enzymes might exist as a complex in the yeast extract. Sucrose gradient analysis of concentrated purified yeast DNA polymerase I preparations demonstrates that the yeast DNA polymerase I does sediment as a complex with DNA primase activity. Two DNA polymerase I peptides estimated at 78,000 and 140,000 Da were found in the complex that were absent from the primase-free DNA polymerase fraction. Rabbit anti-yeast DNA polymerase I antibody inhibits DNA polymerase I but not DNA primase although rabbit antibodies are shown to remove DNA primase activity from solution by binding to the complex. Mouse monoclonal antibody to yeast DNA polymerase I binds to free yeast DNA polymerase I as well as the complex, but not to the free DNA primase activity. These results suggest that these two activities exist as a complex and reside on the different polypeptides. Replication of poly(dT) and single-stranded circular phage DNA by yeast DNA polymerase I and primase requires ATP and dNTPs. The size of the primer produced is 8 to 9 nucleotides in the presence of dNTPs and somewhat larger in the absence of dNTPs. Aphidicolin, an inhibitor of yeast DNA polymerase I, is not inhibitory to the yeast DNA primase activity. The primase activity is inhibited by adenosine 5'-(3-thio)tri-phosphate but not by alpha-amanitin. The association of yeast DNA polymerase I and yeast DNA primase can be demonstrated directly by isolation of the complex on a column containing yeast DNA polymerase I mouse monoclonal antibody covalently linked to Protein A-Sepharose. Both DNA polymerase I and DNA primase activities are retained by the column and can be eluted with 3.5 M MgCl2. Part of the primase activity can be dissociated from DNA polymerase on the column with 1 M MgCl2 and this free primase activity can be detected as poly(dT) replication activity in the presence of Escherichia coli polymerase I.

Animals↗
PubMed1984

Monoclonal antibodies to human terminal transferase.

Human terminal deoxynucleotidyltransferase was used to produce mouse monoclonal antibodies. Three different assays were used to screen for terminal transferase antibodies and antibody-producing hybridoma cells: an enzyme binding assay, an enzyme-linked immunosorbent assay, and a "terminal transferase-specific antibody" cytochemical procedure that allows visualization of the homogeneity of the hybridoma clones producing antibodies to terminal transferase. Of the 12 mouse hybridoma clones isolated, seven produce IgG1 and five produce IgG2a immunoglobulins. Only one of these monoclonal antibodies is inhibitory to human terminal transferase activity. Four of the monoclonal antibodies react with terminal transferase peptides after separation on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, while the remainder appear to recognize only native determinants on the human enzyme. Cross-reactivity studies with purified calf thymus enzyme show that although four of the monoclonal antibodies bind to native enzyme, none react with calf thymus terminal transferase peptides after sodium dodecyl sulfate-polyacrylamide gel electrophoresis, suggesting structural differences within the cross-reactive determinants. A more general survey on the affinity of these monoclonal antibodies to human terminal transferase for the enzyme from other species using an enzyme-linked immunosorbent assay demonstrates that none of the monoclonal antibodies reacts with chicken thymus terminal transferase. The affinity of binding for terminal transferase from other mammals to this panel of monoclonal antibodies varies with the clones as expected, but few bind as strongly as the human enzyme. These results suggest that although antigenic determinants are conserved through evolution, fine structural changes within the determinants do occur.

Animals↗
PubMed1984

Isolation and partial characterization of DNA polymerases from Crithidia fasciculata.

Two types of DNA polymerase activity were partially purified from Crithidia fasciculata. The alpha-type, DNA polymerase A, was of high molecular weight and sensitive to N-ethylmaleimide, whereas the beta-type, DNA polymerase B, was of low molecular weight and resistant to N-ethylmaleimide. Phosphocellulose chromatography revealed multiple peaks of DNA polymerase A activity the properties of which, such as pH optimum, salt sensitivity, utilization of synthetic template-initiator complexes and response to DNA polymerase inhibitors were similar. The response of the C. fasciculata DNA polymerase A enzymes to some of these inhibitors and utilization of poly(rA) X oligo(dT)11 showed these enzymes to be markedly different from mammalian DNA polymerase alpha.

Animals↗
PubMed1984

Molecular cloning of human terminal deoxynucleotidyltransferase.

A cDNA of the human terminal deoxynucleotidyltransferase (TdT; "terminal transferase," EC 2.7.7.31) was isolated from a human lymphoblastoid cell cDNA library in lambda gt 11 by using immunological procedures. Four inserts containing 723 to 939 base pairs were recloned in pBR322 for hybridization and preliminary sequence studies. mRNA selected by hybridization to recombinant DNA was translated to a 58-kDa peptide that specifically immunoprecipitated with rabbit antibodies to calf terminal transferase and mouse monoclonal antibody to human terminal transferase. Blot hybridization of total poly(A)+ RNA from KM3 (TdT+) cells with nick-translated pBR322 recombinant DNA detected a message of about 2000 nucleotides, sufficient to code for the 580 amino acids in the protein. mRNA from terminal transferase- cells gave no signal in hybrid selection or RNA blot hybridization. The complete sequence of the 939-base-pair insert sequence was obtained from deletions cloned in pUC8. The DNA sequence contains an open reading frame coding for 238 amino acids, about 40% of the protein. Three peptides isolated by HPLC from tryptic digests of succinylated 58-kDa calf thymus terminal transferase were sequenced, providing 20, 18, and 22 residues of peptide sequence. A search of the translated sequence of the 939-base-pair insert shows three regions beginning after arginine that have greater than 90% homology with the sequence determined from the calf thymus terminal transferase peptides. These results provide unambiguous evidence that the human terminal transferase sequence has been cloned.

Amino Acid Sequence↗
PubMed1984

DNA replication and repair in Tilapia cells. I. The effect of ultraviolet radiation.

The effect of ultraviolet radiation on a cell line established from the warm water fish Tilapia has been assessed by measuring the rate of DNA synthesis, excision repair, post-replication repair and cell survival. The cells tolerate ultraviolet radiation better than mammalian cells with respect to DNA synthesis, post-replication repair and cell survival. They are also efficient in excision repair, which in other fish cell lines has been found to be at a low level or absent. Their response to the inhibitors hydroxyurea and 1-beta-D-arabinofuranosylcytosine is less sensitive than that of other cell lines, yet the cells seem to have very small pools of DNA precursor.

Animals↗
PubMed1984

Aucubin: potential antidote for alpha-amanitin poisoning.

Aucubin, an iridoid glucoside isolated from Aucuba japonica (Cornaceae), exhibited significant protective activity against alpha-amanitin intoxication in mice. When a single dose of aucubin was administered intraperitoneally, a 50% survival rate was obtained even when the treatment was withheld for 12 hr after alpha-amanitin administration. A possible mechanism of protective activity is partly due to a competitive effect of aucubin on alpha-amanitin inhibition of liver RNA biosynthesis.

Administration, Oral↗
PubMed1983

Polypeptide structure of DNA polymerase I from Saccharomyces cerevisiae.

DNA polymerase I of the yeast Saccharomyces cerevisiae has been purified to near homogeneity. The enzyme sediments under high salt conditions as a band at 7.4 S and two polypeptides of Mr = 140,000 and 110,000 are resolved by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Both polypeptides react with rabbit anti-yeast DNA polymerase I serum and can be shown to be enzymatically active by renaturation in situ after electrophoresis on polyacrylamide gels in the presence of sodium dodecyl sulfate. This high molecular weight form of yeast DNA polymerase I is very sensitive to inhibition by aphidicolin. The biochemical properties of the enzyme and inhibitors that may aid in distinguishing yeast DNA polymerases I and II are also described.

Aphidicolin↗
PubMed1983

Purification and characterization of yeast topoisomerase I.

Yeast topoisomerase I (Mr = 76,000) has been purified to 80% homogeneity using a combination of ion exchange, gel filtration, and DNA-cellulose chromatography. The enzyme was characterized with respect to its ability to relax supercoiled DNA and to catenate nicked circular DNA. Yeast topoisomerase I will remove both positive and negative turns in DNA supercoils in the absence of ATP and magnesium ion. The products of the catenating activity of the enzyme were examined on agarose gels and in the electron microscope. These analyses indicate that yeast topoisomerase I will generate large catenated DNA networks which appear to rearrange to multimeric linear structures upon long incubation time.

DNA Topoisomerases, Type I↗
PubMed1982

Cyclic AMP-dependent phosphorylation of terminal deoxynucleotidyl transferase.

Incubation of human lymphoblastoid cell extracts in the presence of cAMP and ATP produces changes in the chromatographic pattern of terminal transferase activity separated on phosphocellulose columns. Incubation of high molecular weight and low molecular weight preparations of calf thymus terminal transferase with the catalytic subunit of beef cardiac muscle cAMP-dependent protein kinase and [gamma-32P]ATP result in phosphorylation of the 58,000-dalton form of the enzyme and no other lower molecular weight terminal peptides. These results, taken with our earlier results on tissue proteolysis of terminal transferase to lower molecular weight, active forms (Chang, L. M. S., Plevani, P., and Bollum, F. J. (1982) J. Biol. Chem. 257, 5700-5706), resolve the heterogeneity observed with various preparations of the enzyme.

Adenosine Triphosphate↗
PubMed1982

Proteolytic degradation of calf thymus terminal deoxynucleotidyl transferase.

A high molecular weight preparation of terminal transferase containing 58,000- and 44,000-dalton peptides has been purified from calf thymus glands. The relationship of these terminal transferase peptides to the low molecular weight form was established with an immunoblot procedure using rabbit antibody directed against the homogeneous calf thymus low molecular weight terminal transferase (32,000 daltons). The 58,000- and 44,000-dalton enzyme species are each shown to be enzymatically active by renaturation in situ after electrophoresis on polyacrylamide gel in the presence of sodium dodecyl sulfate. These results suggest that the homogeneous terminal transferase previously described is derived from the higher molecular weight species by proteolysis during fractionation. Controlled degradation of the high molecular weight calf thymus terminal transferase with trypsin produces fully active enzyme containing alpha- and beta-peptides similar to those found in the 32,000-dalton species. Isoelectric focusing experiments show a decrease of isoelectric pH of the enzyme with proteolysis.

Animals↗
PubMed1982

Evolutionary conservation of DNA polymerase beta structure.

An immunological procedure that uses antiserum against homogeneous calf thymus DNA polymerase beta to detect immunoreactive peptides on NaDodSO4/polyacrylamide gel electrophoresis demonstrates a high degree of conservation of protein sequence and molecular weight for this enzyme, from parastic protozoans to man. By renaturation of DNA polymerase activity in situ after electrophoresis, the enzymatically active peptides are shown to correspond to the immunoreactive peptides. The persistence of sequence and molecular weight for the catalytic peptide of DNA polymerase beta through eons of evolutionary time suggests an essential role for this enzyme in DNA metabolism of complex cells.

Animals↗
PubMed1981

Immunological detection of a conserved structure for terminal deoxynucleotidyltransferase.

The polypeptide structure of terminal transferase in crude extracts of thymus or cultured cells was examined by electrophoresis on polyacrylamide gels in the presence of sodium dodecyl sulfate, electrophoretic transfer of separated peptides to nitrocellulose, specific labeling with rabbit anti-calf thymus terminal transferase, and visualization with an immunoperoxidase reaction. The major form of terminal transferase detected in crude extracts or enzyme fractions after phosphocellulose chromatography is a single 58,000- to 60,000-dalton peptide for calf thymus, rat thymus, mouse thymus, chicken thymus, cat thymus, human lymphoblastoid cells, and mouse lymphoblastoid cells. Since the anti-calf thymus terminal transferase antibody was prepared against a homogeneous calf thymus enzyme consisting of two polypeptide chains in a hydrodynamic structure of Mr = 32,000, these results suggest that the homogeneous calf thymus enzyme preparation is a proteolytically degraded form of the 58,000-dalton peptide. Terminal transferase peptides from human, bovine, rat, chicken, cat, and mouse are immunologically related and have similar conserved polypeptide structure.

Animals↗
PubMed1981

Immunological reagents for comparisons of DNA polymerase-alpha and DNA polymerase-beta.

Antibodies to homogeneous calf thymus DNA polymerase-beta and calf thymus DNA polymerase-alpha preparations were raised in rabbits. The antiserum against calf thymus DNA polymerase-beta cross-reacts with all vertebrate DNA polymerase-beta preparations tested, but does not cross-react with trypanosome DNA polymerase-beta, DNA polymerase-gamma, terminal transferase, yeast DNA polymerases, and Escherichia coli DNA polymerase I. The antibodies against calf thymus DNA polymerase-alpha cross-react with DNA polymerase-alpha from mouse, human, and chicken, but do not cross-react with DNA polymerase-alpha from sea urchin embryos and Drosophila embryos, DNA polymerase-beta, DNA polymerase-gamma, terminal transferase, yeast DNA polymerases, and E. coli DNA polymerase I.

Animals↗
PubMed1981

Intracellular localization of DNA polymerase alpha.

Immunoglobulin (IgG) and the F(ab')2 fragment of IgG were prepared from serum of a rabbit immunized with purified calf thymus DNA polymerase alpha (deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7). An indirect immunofluorescent method based on these reagents was used to detect the intracellular localization of DNA polymerase alpha in primary fetal bovine fibroblasts. The results show that the bulk of DNA polymerase alpha is located in the perinuclear region of the cytoplasm. Immunofluorescent staining of cytoplast and Ficoll-Paque gradient-purified karyoplast fragments resulting from cytochalasin enucleation show the presence of DNA polymerase alpha in cytoplasts and the virtual absence of the enzyme in the nucleus of the karyoplast itself. The implication of this unusual intracellular location for DNA polymerase alpha is discussed.

Animals↗