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L M Chang

Publications and source records attributed to L M Chang.

At least 55 records · Page 3Linked to original sources
PubMed1980

Purification and characterization of two forms of DNA-dependent ATPase from yeast.

Two forms of DNA-dependent ATPase activity have been purified from yeast extracts. The two ATPases differ from each other in chromatographic properties and heat stabilities but have similar molecular weight and reaction properties. DNA-dependent ATPase I has been purified to near homogeneity, while DNA-dependent ATPase II is only partially purified. The two ATPases from yeast are related structurally since antiserum raised against ATPase I cross-react against ATPase II. Yeast DNA-dependent ATPase I has a native molecular weight of about 68,000 and consists of a single polypeptide chain. ATPase II also sediments on sucrose gradient as a 68,000-dalton protein. Both yeast DNA-dependent ATPases hydrolyze dNTPs and rNTPs to their corresponding nucleoside diphosphates and orthophosphate, but dATP and ATP are preferred substrates. In addition to nucleoside triphosphates, both enzymes require a divalent cation and a polynucleotide for activity. Single-stranded DNAs and polydeoxynucleotides are the most effective co-substrates for yeast DNA-dependent ATPases. Addition of yeast DNA-dependent ATPases to DNA synthesis system containing yeast DNA polymerases does not significantly stimulate the rate of DNA synthesis.

Adenosine Triphosphatases↗
PubMed1980

DNA polymerases in parasitic protozoans differ from host enzymes.

Analysis of extracts of the bloodstream forms of Trypanosoma brucei showed that both DNA polymerase-alpha and DNA polymerase-beta activities were present. The detection of DNA polymerase-beta in T. brucei demonstrates the presence of this enzyme in unicellular organisms. DNA polymerase-beta is present also in Leishmania mexicana. The DNA polymerases in T. brucei are immunologically distinct from the host enzymes. The structural differences between the parasite and the host enzymes could be exploited for the development of agents to combat parasitic diseases.

Animals↗
PubMed1978

Initiation of enzymatic DNA synthesis by yeast RNA polymerase I.

In vitro DNA synthesis by yeast DNA polymerase I can be initiated by partially purified yeast RNA polymerases in the presence or absence of rNTPs. Homogeneous yeast RNA polymerase I initiates DNA synthesis by yeast DNA polymerase I on single-stranded DNA templates only in the presence of all four rNTPs. A protein capable of initiating enzymatic DNA synthesis on single-stranded DNA in the absence of rNTPs has also been separated from partially purified yeast RNA polymerase I fractions. Analysis of the RNA polymerase I initiated replication products of phage fd DNA on alkaline sucrose gradients showed noncovalent linkage between the newly synthesized DNA and the template. Isopycnic analyses of the ribonucleotide initiated fd DNA replication products demonstrated covalent linkage between the initiator RNA and newly synthesized DNA. Results from 32P-transfer experiments confirmed the covalent linkage between RNA and DNA chains and showed the presence of all four ribo- and deoxyribonucleotides at the RNA--DNA junctions. The ribonucleotide found most frequently at the RNA--DNA junction is uridylate and the purine deoxynucleotides occur more frequently than pyrimidine deoxynucleotides.

DNA↗
PubMed1977

DNA polymerases from bakers' yeast.

Two DNA polymerases are present in extracts of commercial bakers' yeast and wild type Saccharomyces cerevisiae grown aerobically to late log phase. Yeast DNA polymerase I and yeast DNA polymerase II can be separated by DEAE-cellulose, hydroxylapatite, and denatured DNA-cellulose chromatography from the postmitochondrial supernatants of yeast lysates. The yeast polymerases are both of high molecular weight (greater than 100,000) but are clearly separate species by the lack of immunological cross-reactivity. Analysis of associated enzyme activities and other reaction properties of yeast DNA polymerases provides additional evidence for distinguishing the two species. Enzyme I has no associated nuclease activity but does carry out pyrophosphate exchange and pyrophosphorolysis reactions, and has an associated 3'-exonuclease activity. Enzyme I does not degrade deoxynucleoside triphosphates and cannot utilize a mismatched template. Enzyme II does carry out a template-dependent deoxynucleoside triphosphate degradation reaction and can excise mismatched 3'-nucleotides from suitable template systems. Earlier studies have shown that both Enzyme I and Enzyme II are inhibited by N-ethylmaleimide. The yeast enzymes are not identical to any known eukaryotic or prokaryotic DNA polymerases. In general, Enzyme I appears to be most similar to eukaryotic DNA polymerase alpha and Ezyme II exhibits properties of prokaryotic DNA polymerases II and III.

DNA Polymerase I↗
PubMed1977

Enzymatic initiation of DNA synthesis by yeast DNA polymerases.

Partially purified yeast RNA polymerases (RNA nucleotidyltransferases) initiate DNA synthesis by yeast DNA polymerase (DNA nucleotidyltransferase) I and to a lesser extent yeast DNA polymerase II in the replication of single-stranded DNA. The enzymatic initiation of DNA synthesis on phage fd DNA template occurs with dNTPs alone and is further stimulated by the presence of rNTPs in DNA polymerase I reactions. The presence of rNTPs has no effect on the RNA polymerase initiation of the DNA polymerase II reaction. RNA polymerases I and III are more efficient in initiation of DNA synthesis than RNA polymerase II. Analyses of the products of fd DNA replication show noncovalent linkage between the newly synthesized DNA and the template DNA, and covalent linkage between the newly synthesized RNA and DNA.

Amanitins↗
PubMed1976

DNA polymerase of Dictyostelium discoideum.

Only one molecular weight species of DNA polymerase was found in different developmental stages of the eukaryotic microorganism Dictyostelium discoideum. The molecular weight of this DNA polymerase is estimated to be about 127 000 by sucrose gradient centrifugation. The enzyme is present in all stages of growth and development, including dormant spores. All DNA polymerase activity is lost upon incubation of the crude extract with N-ethylmaleimide. The reaction properties, molecular weight and N-ethylmaleimide sensitivity of the D. discoideum DNA polymerase are similar to those of the DNA polymerase-alpha from mammalian sources.

Binding Sites↗
PubMed1976

Phylogeny of DNA polymerase-beta.

Analyses of various organisms for DNA polymerase-beta activity show that the enzyme is widely distributed in cells from multicellular animals but absent in bacteria, plants, and protozoa. These results suggest that DNA polymerase-beta may have evolved with the development of metazoan forms. Further evolutionary changes of the enzyme protein may account for some of the minor differences in properties of the enzyme in various organisms.

Animals↗