• Korean Journal of Microbiology
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• v.52 no.1
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• pp.116-119
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• 2016

Stable maintenance of telomere is required for cell proliferation and survival. Although telomerase is the primary means for telomere maintenance, recombination is another important pathway to maintain telomeres. In this study, we developed a genetic assay for telomere recombination using the internal $TG_{1-3}$ repeats present in subtelomeric regions of yeast. The recombination frequencies were dependent on the presence of the internal $TG_{1-3}$ repeats. PCR amplification of the regions near URA3 and CAN1 markers using genomic DNA isolated from $FOA^rCan^r$ colonies indicated that each isolate had lost the chromosome end including the markers. In addition, the recombination frequencies increased with longer internal $TG_{1-3}$ repeats. Our results suggest that the $FOA^rCan^r$ colony formation is the consequence of recombination between the internal and terminal $TG_{1-3}$ repeats.

• BMB Reports
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• v.51 no.11
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• pp.578-583
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• 2018

Telomeres are specialized nucleoprotein complexes that function to protect eukaryotic chromosomes from recombination and erosion. Several telomere binding proteins (TBPs) have been characterized in higher plants, but their detailed in vivo functions at the plant level are largely unknown. In this study, we identified and characterized OsTRFL1 (Oryza sativa Telomere Repeat-binding Factor Like 1) in rice, a monocot model crop. Although OsTRFL1 did not directly bind to telomere repeats $(TTTAGGG){_4}$ in vitro, it was associated with telomeric sequences in planta. OsTRFL1 interacted with rice TBPs, such as OsTRBF1 and RTBP1, in yeast and plant cells as well as in vitro. Thus, it seems likely that the association of OsTRFL1 with other TBPs enables OsTRFL1 to bind to telomeres indirectly. T-DNA inserted OsTRFL1 knock-out mutant rice plants displayed significantly longer telomeres (6-25 kb) than those (5-12 kb) in wild-type plants, indicating that OsTRFL1 is a negative factor for telomere lengthening. The reduced levels of OsTRFL1 caused serious developmental defects in both vegetative and reproductive organs of rice plants. These results suggest that OsTRFL1 is an essential factor for the proper maintenance of telomeres and normal development of rice.

• Molecules and Cells
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• v.26 no.1
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• pp.93-99
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• 2008

Transcriptional silencing is regulated by promoter methylation and histone modifications such as methylation and acetylation. We constructed a Schizosaccaromyces pombe reporter strain, KCT120a, to identify modifiers of transcriptional silencing, by inserting the $ura4^+$ gene into a heterochromatic telomere region. Two compounds inhibited the activity of histone deacetylases, induced acetylation of histone H3 and caused apoptotic cell death in HeLa cells. Expression of gelsolin and $p21^{waf1/cip1}$ also increased, as it does in response to HDAC inhibitors such as TSA. Therefore, these compounds appear to be potent inhibitors of HDACs, and hence potential anti-cancer drugs. Our observations suggest that a yeast cell-based assay system for transcriptional silencing may be useful for identifying histone deacetylase inhibitors and other agents affecting chromatin remodeling.

• BMB Reports
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• v.52 no.3
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• pp.175-180
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• 2019

Telomeres are nucleoprotein complexes at the physical ends of linear eukaryotic chromosomes. They protect the chromosome ends from various external attacks to avoid the loss of genetic information. Telomeres are maintained by cellular activities associated with telomerase and telomere-binding proteins. In addition, epigenetic regulators have pivotal roles in controlling the chromatin state at telomeres and subtelomeric regions, contributing to the maintenance of chromosomal homeostasis in yeast, animals, and plants. Here, we review the recent findings on chromatin modifications possibly associated with the dynamic states of telomeres in Arabidopsis thaliana.

• Journal of Life Science
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• v.26 no.6
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• pp.646-650
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• 2016

The influence of chromosome number on cell growth and cell aging was investigated in various yeast strains that have many artificial chromosomes constructed using a chromosome manipulation technique. Host strain FY833 and the YKY18, YKY18R, YKY24, and YKY30 strains harboring 16 natural chromosomes, 18 chromosomes, 18 chromosomes containing rDNA chromosome, 24 chromosomes, and 30 chromosomes, respectively, were used, and the specific growth rate of each strain was compared. The specific growth rates in the YKY18 and YKY24 strains were indistinguishable from that in the host strain, while those of the YKY18R and YKY30 strains were reduced to approximately 25% and 40% of the host strain level, respectively. Subsequently, the replicative life span was examined to investigate the relationship between the number of chromosomes and cell aging, and the life span was decreased to approximately 14% and 45% of the host strain level in the YKY24 and YKY30 strains, respectively. Moreover, telomere length, well known as a senescence factor, was shorter and more diversified in the strain, showing decreased life span. Therefore, these results suggest the possibility that an increase in the number of chromosomes containing artificial chromosomes caused cell aging, and we expected these observations would be applied to improve industrial strain harboring of versatile and special artificial chromosomes.

• Journal of Life Science
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• v.30 no.9
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• pp.819-825
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• 2020

All living organisms exhibit the characteristics of aging, such as skin wrinkle formation, muscle degeneration, cataracts, and hair graying as the number of aged cells increases over time. Senescence, which is known as a key cause of aging, is directly related to the aging of living organisms because cells are aged by external and internal factors and eventually cell proliferation is stopped. Senescence is caused by the gradual shortening of the telomere with cell division, and lifespan is determined by the length of the telomere. Recently, it has been found that the histone deacetylase, which can influence gene expression, is not only involved in yeast but also deeply involved in anti-aging mechanisms in both C. elegans and humans. It was also discovered that old cells play a decisive role in the aging phenomenon, and it has been reported that it is possible to promote the proliferation of young cells and delay aging by removing these senescent cells from the inside. Therefore, in order to develop potential anti-aging agents in the future, research should begin with an in-depth study of telomerase activators, sirtuin activators, and senolytics.

• Biotechnology and Bioprocess Engineering:BBE
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• v.5 no.1
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• pp.1-6
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• 2000

For the rapid selection of higher recombinant hirudin producing strain in a methylotrophic yeast Hansenula polymorpha, a multiple gene integration and dose-dependent selection vector, based on a telomere-associated ARS and a bacterial aminoglycoside 3-phosphotransferase (aph) gene, was adopted. Two hirudin expression cassettes (HV1 and HV2) were constructed using the MOX promoter of H. polymorpha and the mating factor $\alpha$ secretion signal of S. cerevisiae. Multiple integrants of a transforming vector containing hirudin expression cassettes were easily selected by using an antibiotic, G418. Hirudin expression level and integrated plasmid copy number of the tested transformants increased with increasing the concentration of G418 used for selection. The expression level of HV1 was consistently higher than that of HV2 under the similar conditions, suggesting that the gene context might be quite important for the high-level gene expression in H. polymorpha. The highest hirudin producing strain selected in this study produced over 96 mg/L of biologically active hirudin in a 500-mL flask and 165 mg/L in a 5-L fermentor.

• Korean Journal of Plant Tissue Culture
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• v.25 no.6
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• pp.453-475
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• 1998

During the 100 years since the initial discovery of meiotic phenomenon many brilliant aspects have been elucidated, but further researches based on light microscopy alone as an experimental tool have been found to have some limits and shortcomings. By the use of electron microscopy and armed with the advanced knowledges on modern genetics and biochemistry it has been possible to applu molecular technology in gaining information on the detailed aspects of meiosis. As synapsis takes place, a three-layered proteinous structure called the synatonemal complex starts to form in the space between the homologous chromosomes. To be more precise, it begins to form along the paired chromosomes early in the prophase I of meiotic division. The mechanism that leads to precise point-by-point pairing between homologous chromocomes division. The mechamism that leads to precise point-by-point pairing between homologous chromosomes remains to be ascertained. Several items of information, however, suggest that chromsome alignment leading to synapsis may be mediated somehow by the nuclear membrane. Pachytene bivalents in eukaryotes are firmly attached to the inner niclear membrane at both termini. This attached begins with unpaired leptotene chromosomes that already have developed a lateral element. Once attached, the loptotene chromosomes begin to synapse. A number of different models have been proposed to account for genetic recombination via exchange between DNA strands following their breakage and subsequent reunion in new arrangement. One of the models accounting for molecular recombination leading to chromatid exchange and chiasma formation was first proposed in 1964 by Holliday, and 30 years later still a modified version of his model is favored. Nicks are made by endomuclease at corresponding sites on one strant of each DNA duplex in nonsister chromatid of a bivalent during prophase 1 of meiosis. The nicked strands loop-out and two strands reassociate into an exchanged arrangement, which is sealed by ligase. The remaining intact strand of each duplex is nicked at a site opposite the cross-over, and the exposed ends are digested by exonuclease action. Considerable progress has been made in recent years in the effort to define the molecular and organization features of the centromere region in the yeast chromosome. Centromere core region of the DNA duplex is flanked by 15 densely packed nucleosomes on ons side and by 3 packed nucleosomes on the other side, that is, 2000 bp on one side and 400 400 bp in the other side. All the telomeres of a given species share a common DNA sequence. Two ends of each chromosome are virtually identical. At the end of each chromosome there exist two kinds of DNA sequence" simple telpmeric sequences and telpmere-associated sequencies. Various studies of telomere replication, function, and behabior are now in progress, all greatly aided by molecular methods. During nuclear division in mitosis as well as in meiosis, the nucleili disappear by the time of metaphase and reappear during nuclear reorganizations in telophase. When telophase begins, small nucleoli form at the NOR of each nucleolar-organizing chromosome, enlarge, and fuse to form one or more large nucleoli. Nucleolus is a special structure attached top a specific nucleolar-organizing region located at a specific site of a particular chromosome. The nucleolus is a vertical factory for the synthesis of rRNAs and the assenbly of ribosome subunit precursors.sors.