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Kinetic analysis of avian sarcoma virus integrase in the presteady-stateBao, Kogan K. 19 September 2002 (has links)
Integrase catalyzes insertion of a retroviral genome into the host chromosome.
Following reverse transcription, integrase binds specifically to the ends of the duplex retroviral
DNA, endonucleolytically cleaves two nucleotides from each 3'-end (the processing activity),
and inserts these ends into the host DNA (the joining activity) in a concerted manner.
Additionally, it has been observed that integrase can catalyze the removal of inserted viral ends
(the disintegration activity) in vitro. Presteady-state experiments were performed using synapsed
substrates to probe the processing reaction and a disintegration substrate to determine the
number of protomers in a functional multimeric complex. In single-turnover studies, a novel
"splicing" reaction was observed that revealed complications with accurate quantification of
enzymatic activity using the synapsed substrates. The splicing reaction was further used to gain
insight into the selection of nucleophiles and electrophiles at the binding site. To reduce the
complexity introduced by the integrase-catalyzed splicing reaction, 5'-5' reverse-polarity
synapsed substrates were designed that were not susceptible to the splicing reaction and that
allowed direct comparison of LTR ends simultaneously bound at the active site. Analysis of the
presteady-state assays using these reverse-polarity substrates revealed that the concurrent binding
of the biologically relevant U3/U5 combination of viral ends facilitates maximal activity of the
processing reaction. A disintegration substrate was used in presteady-state active site titrations to
determine a reaction stoichiometry of four integrase protomers per one substrate molecule for
the disintegration reaction. A tetrameric active complex was then confirmed using atomic force
microscopy to image integrase-DNA complexes during the first catalytic turnover. The
observed increase of the tetramer population in the presence of substrate DNA demonstrates that
the binding of the disintegration substrate induces assembly of the active tetramer and suggests
that tetramer assembly may be an integral and dynamic component of the catalytic pathway. / Graduation date: 2003
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Cucumber mosaic virus-induced particulate RNA replicase / by Dalip Singh GillGill, Dalip Singh January 1983 (has links)
Bibliography: leaves 116-117 / viii, 131, [82] leaves, [20] leaves of plates : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1983
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Organization of the T4 dNTP synthetase complex at DNA replication sitesKim, JuHyun 02 February 2005 (has links)
With respect to a multienzyme complex of deoxyribonucleoside triphosphate
(dNTP) synthesis somehow juxtaposed with DNA replication sites, our laboratory
has demonstrated the existence of a multienzyme complex in T4-infected E. coli,
named the T4 dNTP synthetase complex, but the idea of direct linkage of dNTP
synthesis to DNA replication and organization of the complex has not been well
established. This study had two objectives. The first objective was to test the specific
hypothesis that gp32, the single-stranded DNA binding protein encoded by gene 32,
plays a role in recruiting enzymes of dNTP synthesis to the replisome and in
organizing the dNTP synthetase complex. By use of two newly created gene 32
mutants along with several experimental approaches, DNA-cellulose
chromatography, coimmunoprecipitation, and glutathione-S-transferase pull downs,
interactions of gp32 with thymidylate synthase (gptd), ribonucleotide reductase
(gpnrdA/B), and E. coli NDP kinase have been identified. These results support the
hypothesis that gp32 helps to recruit enzymes of dNTP synthesis to DNA replication
sites.
As the second objective, I investigated contributions of two host proteins, E. coli
nueleoside diphosphate kinase (NDP kinase) and adenylate kinase (Adk), to the
organization of the complex. As an important step to understand roles of E. coli NDP
kinase in the complex, I identified direct interactions of E. coli NDP kinase with
gpnrdA/B, dCMP hydroxymethylase (gp42), and dihydrofolate reductase (gpfrd) by
means of coimmunoprecipitation and glutathione-S-transferase pull-down
experiments. Interestingly, these interactions were influenced by the presence of
substrate nucleotides or an analog for E. coli NDP kinase, suggesting that metabolite
flux may affect the preference of E. coli NDP kinase binding to enzymes in the
complex in vivo. Meanwhile, Adk involvement in DNA precursor synthesis has been
suggested, particularly in phage T4-infected E. coli, from observations of increased
thermostability of temperature-sensitive Adk in situ. The involvement of E. coil Adk
in the complex was demonstrated by identifying some proteins of the T4 dNTP
synthetase complexgp42, dNMP kinase (gpl), gpfrd, and E. coli NDP
kinasedirectly interacting with Adk, implying that E. coil Adk would be properly
located in the complex to efficiently carry out the conversion of dNDPs to dNTPs.
This implication was supported by measurements of T4 DNA synthesis.
Taken together, this research strongly supports the idea of connection of dNTP
synthesis to DNA replication and allows us to take a step toward understanding the
organization of the complex at DNA replication sites. / Graduation date: 2005
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