• Korean Journal of Microbiology
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• v.25 no.1
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• pp.34-39
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• 1987

To study the replication process of the single-stranded DNA parvovirus KBSH-isolated from normal human cell cultures-in actively dividing embryonic swine kidney cells, amount of the synthesized viral hemagglutination (HA) antigen and the overall rate of viral double-stranded replicative form(RF) DNA synthesis were wxamined. The initiation of viral RF KNA synthesis and the decrease of host DNA synthesis rate in viral infected cells occurred almost same time at 15-16 hour post infection(PI). And the release of viral HA antigen to media followed at 24 hour PI, concurrently the overall rate of viral RF DNA synthesis reaching its maximum. Evidence is presented which indicates that successful performance of viral RF DNA replication requires proteins synthesized in viral infected cells at 10-14 hour PI.

• Proceedings of the Korean Society for Applied Microbiology Conference
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• 2003.06a
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• pp.204-207
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• 2003

• Biotechnology and Bioprocess Engineering:BBE
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• v.6 no.4
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• pp.231-236
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• 2001

How much do we know about the biology of aging from cell culture studies Most normal somatic cells have a finite potential to divide due to a process termed cellular or replicative senescence. A growing body evidence suggests that senescence evolved to protect higher eu-karyotes, particularly mammals, from developing cancer, We now know that telomere shortening due to the biochemistry of DNA replication, induces replicative senescence in human cells. How-ever in rodent cells, replicative senescence occurs despite very long telomeres. Recent findings suggest that replicative senescence is just the tip of the iceberg of a more general process termed cellular senescence. It appears that cellular senescence is a response to potentially oncogenic in-sults, including oxidative damage. In young orgainsms, growth arrest by cell senescence sup-presses tumor development, but later in life, due to the accumulation of senescent cells which se-cret factors that can disrupt tissues during aging, cellular senescence promotes tumorigenesis. Therefore, antagonistic pleiotropy may explain, if not in whole the apparently paradoxical effects of cellular senescence, though this still remains an open question.

• BMB Reports
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• v.29 no.1
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• pp.63-67
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• 1996

In order to elucidate the molecular mechanism of plasmid incompatibility of broad host-range plasmid R1162, the plasmid-encoded replication protein RepIB was purified and tested for binding to the 20 bp direct repeat (DR) DNA sequence which is reiterated 3 and 1/2 times within the replicative origin of the plasmid. The RepIB protein specifically binds to the DR DNA. Point mutations in the DR which affect expression of plasmid incompatibility also coordinately affect binding. These results indicate that the incompatibility of broad host-range plasmid R1162 is exerted by the DR DNA by titrating the essential replication protein RepIB.

• Korean Journal of Veterinary Research
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• v.32 no.4
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• pp.597-603
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• 1992

To elucidate the molecular genetical properties of the canine parvoviruses isolated from the diseased puppies in the regions of Kyunggi and Chungnam provinces, the replicative form (RF) DNA of four field isolates were compared with those of two attenuated vaccine strains and a reference strains of CPV by restriction endonuclease analysis (REA). REA by Hinf I showed that three CPV isolates except CPV-V15 had an identical banding pattern with two vaccine strains, one standard strain and feline panleukopenia virus (FPLV). In CPV-V15 strain the fourth fragment of DNA with 800 bp was deleted. REA by Bgl II and Pst I indicated that CPV-V15 and FPLV had a bigger second fragment than those of the other strains of CPV. Meanwhile REA by Bam HI revealed that all the field isolates and vaccine strains used in this experiment showed similar banding patterns.

• Nutrition Research and Practice
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• v.1 no.2
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• pp.105-112
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• 2007

Ascorbic acid has been reported to extend replicative life span of human embryonic fibroblast (HEF). Since the detailed molecular mechanism of this phenomenon has not been investigated, we attempted to elucidate. Continuous treatment of HEF cells with ascorbic acid at ($200{\mu}M$) from 40 population doubling (PD) increased maximum PD numbers by 18% and lowered $SA-{\beta}-gal$ positive staining, an aging marker, by 2.3 folds, indicating that ascorbic acid extends replicative life span of HEF cells. Ascorbic acid treatment lowered DCFH by about 7 folds and Rho123 by about 70%, suggesting that ascorbic acid dramatically decreased ROS formation. Ascorbic acid also increased aconitase activity, a marker of mitochondrial aging, by 41%, indicating that ascorbic acid treatment restores age-related decline of mitochondrial function. Cell cycle analysis by flow cytometry revealed that ascorbic acid treatment decreased G1 population up to 12%. Further western blot analysis showed that ascorbic acid treatment decreased levels of p53, phospho-p53 at ser 15, and p21, indicating that ascorbic acid relieved senescence-related G1 arrest. Analysis of AP (apurinic/apyrimidinic) sites showed that ascorbic acid treatment decreased AP site formation by 35%. We also tested the effect of hydrogen peroxide treatment, as an additional oxidative stress. Continuous treatment of $20{\mu}M$ of hydrogen peroxide from PD 40 of HEF cells resulted in premature senescence due to increased ROS level, and increased AP sites. Taken together, the results suggest that ascorbic acid extends replicative life span of HEF cells by reducing mitochondrial and DNA damages through lowering cellular ROS.

• Journal of Ginseng Research
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• v.16 no.3
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• pp.210-216
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• 1992

The effect of saponin extracted from Panax grneng CA Meyer on DNA repair and replicative DNA synthesis were examined in CHO-Kl cells cotreated with benzo(a)pyrene and rat liver S-15 fraction. The DNA strand breaks inititated by benzo(a)pyrene metabolites were measured by alkaline election technique. The addition of ginseng saponin to the culture media resulted in decrease of benzo(a)pyrene-induced DNA strand breaks, and restored the suppressed-semiconservative-DNA-synthesis by the carcinogen. DNA repair synthesis in the damaged cells was also elevated by the ginseng treatment when the repairing activites were measured for the (3H)-thymidine incorporation into the carcinogen damaged cellular DNk Comparative analysis of DNA-adduces of benzo(a)pyrene metabortes in microsomes suggested that ginseng saponin treatment in rats reduced the formation of electrophilic metabolites of benzo (a)-pyrene in the rat liver microsomes.

• Journal of Life Science
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• v.25 no.6
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• pp.724-731
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• 2015

Mesenchymal stem cells (MSCs) are characterized by their multipotency capacity, which allows them to differentiate into diverse cell types (bone, cartilage, fat, tendon, and neuron-like cells) and secrete a variety of trophic factors (ANG, FGF-2, HGF, IGF-1, PIGF, SDF-1α, TGF-β, and VEGF). MSCs can be easily isolated from human bone-marrow, fat, and umbilical-cord tissues. These features indicate that MSCs might be of use in stem-cell therapy. However, MSCs undergo cellular senescence during long-term expansion, and this is accompanied by functional declines in stem-cell potency. In the human body, because of their senescence and declines in their microenvironmental niches stem cells fail to maintain tissue homeostasis, and as a result, senescent cells accumulate in tissues. This can lead to age-related diseases, including degenerative disorders and cancers. Recent studies suggest that the number of histone modifications to stem cells’ genomes and aberrant alterations to their DNA methylation increase as stem cells progress into senescence. These epigenetic alterations have been partly reversed with treatments in which DNA methyltransferase (DNMT) inhibitors or histone deacetylase (HDAC) inhibitors are introduced into replicative senescent-MSCs. This review focuses on epigenetic alteration in replicative senescent-MSCs and explains how epigenetic modifications are widely associated with stem-cell senescences such as differentiation, proliferation, migration, calcium signaling, and apoptosis.

• Journal of Life Science
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• v.14 no.1
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• pp.131-140
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• 2004

T7 bacteriophage gp4 is the replicative DNA helicase that unwinds double-stranded DNA by utilizing dTTP hydrolysis energy. The quaternary structure of the active form of T7 helicase is a hexameric ring with a central channel. Single-stranded DNA passes through the central channel of the hexameric ring as the helicase translocates $5'\rightarrow3'$ along the single-stranded DNA. The DNA unwinding was measured by rapid kinetic methods and showed a lag before the single-stranded DNA started to accumulate exponentially. This behavior was analyzed by a kinetic stepping model for the unwinding process. The observed lag phase increased as predicted by the model with increasing double-stranded DNA length. Trap DNA added in the reaction had no effect on the amplitudes of double-stranded DNA unwound, indicating that the $\tau7$ helicase is a highly processive helicase. Global fitting of the kinetic data to the stepping model provided a kinetic step size of 10-11 bp/step with a rate of $3.7 s^{-1}$ per step. Both the mechanism of DNA unwinding and dTTP hydrolysis and the coupling between the two are unaffected by temperature from $4∼37^{\circ}C$. Thus, the kinetic stepping for dsDNA unwinding is an inherent property of tile replicative DNA helicase.

• Journal of Microbiology and Biotechnology
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• v.8 no.6
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• pp.650-655
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• 1998

The chromosomal DNA fragment from Phaffia rhodozyma CBS 6938 which is able to autonomously replicate in the yeast Saccharomyces cerevisiae was cloned on an integrative URA3 plasmid. Its minimal fragment exhibiting autonomously replicating activiy in the S. cerevisiae gave a higher frequency transformation efficiency than that found for centromere-based plasmid, and enabled extrachromosoma1ly stable transmission of the plasmids in one copy per yeast cell under non-selective culture condition. The 836-bp DNA element lacked an ORF and did not contain any acceptable match to an ARS core consensus. Sequence analysis, however, displayed a cluster of three hairpin-Ioop-sequences with individual $\triangle {G_{25}}^{\circ}C$ free energy value of -10.0, -17.5, and -17.0 kcal. $mor^{-l}$as well as a 9-bp sequence with two base pair mismatches to the S. cerevisiae/E. coli gyrase-binding site. This 836-bp sequence also included one 7-bp sequence analogous to the core consensus of centromeric DNA element III (CDEIII) of S. cerevisiae, but CDEIII-like 7 bp sequence alone did not give a replicative function in this yeast.