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Przanowska RK, Chen Y, Uchida TO, Shibata E, Hao X, Rueda IS, Jensen K, Przanowski P, Trimboli A, Shibata Y, Leone G, Dutta A. Endo-reduplication in mouse liver after conditional mutation of ORC2 and combined mutation of ORC1 and ORC2. bioRxiv 2024:2024.04.04.588006. [PMID: 38617300 PMCID: PMC11014565 DOI: 10.1101/2024.04.04.588006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/16/2024]
Abstract
The six subunit Origin Recognition Complex (ORC) is essential for loading MCM2-7 at origins of DNA replication to promote initiation of DNA replication in organisms ranging from S. cerevisiae to humans. In rare instances, as in cancer cell-lines in culture with mutations in ORC1 , ORC2 or ORC5 , or in endo-reduplicating mouse hepatocytes in vivo without ORC1 , DNA replication has been observed in the virtual absence of individual ORC subunits. Although ORC1 is dispensable in the mouse liver for endo-reduplication, because of the homology of ORC1 with CDC6, it could be argued that CDC6 was substituting for ORC1 to restore functional ORC. Here, we have created mice with a conditional deletion of ORC2 , to demonstrate that mouse embryo fibroblasts require ORC2 for proliferation, but that the mouse hepatocytes can carry out DNA synthesis in vitro and endo-reduplicate in vivo , despite the deletion of ORC2 . Combining the conditional mutation of ORC1 and ORC2 revealed that the mouse liver can still carry out endo-reduplication despite the deletion of the two genes, both during normal development and after partial hepatectomy. Since endo-reduplication, like normal S phase replication, requires the presence of MCM2-7 on the chromatin, these results suggest that in primary hepatocytes there is a mechanism to load sufficient MCM2-7 to carry out effective DNA replication despite the virtual absence of two subunits of ORC.
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2
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Sanada S, Maekawa M, Tate S, Nakaoka H, Fujisawa Y, Sayama K, Higashiyama S. SPOP is essential for DNA replication licensing through maintaining translation of CDT1 and CDC6 in HaCaT cells. Biochem Biophys Res Commun 2023; 651:30-38. [PMID: 36791496 DOI: 10.1016/j.bbrc.2023.02.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Accepted: 02/03/2023] [Indexed: 02/05/2023]
Abstract
Speckle-type pox virus and zinc finger (POZ) protein (SPOP), a substrate recognition receptor for the cullin-3/RING ubiquitin E3 complex, leads to the ubiquitination of >40 of its target substrates. Since a variety of point mutations in the substrate-binding domain of SPOP have been identified in cancers, including prostate and endometrial cancers, the pathological roles of those cancer-associated SPOP mutants have been extensively elucidated. In this study, we evaluated the cellular functions of wild-type SPOP in non-cancerous human keratinocyte-derived HaCaT cells expressing wild-type SPOP gene. SPOP knockdown using siRNA in HaCaT cells dramatically reduced cell growth and arrested their cell cycles at G1/S phase. The expression of DNA replication licensing factors CDT1 and CDC6 in HaCaT cells drastically decreased on SPOP knockdown as their translation was inhibited. CDT1 and CDC6 downregulation induced p21 expression without p53 activation. Our results suggest that SPOP is essential for DNA replication licensing in non-cancerous keratinocyte HaCaT cells.
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Affiliation(s)
- Sayoko Sanada
- Department of Dermatology, Ehime University Graduate School of Medicine, Toon, Ehime, 791-0295, Japan; Department of Biochemistry and Molecular Genetics, Ehime University Graduate School of Medicine, Toon, Ehime, 791-0295, Japan
| | - Masashi Maekawa
- Department of Biochemistry and Molecular Genetics, Ehime University Graduate School of Medicine, Toon, Ehime, 791-0295, Japan; Division of Cell Growth and Tumor Regulation, Proteo-Science Center, Ehime University, Toon, Ehime, 791-0295, Japan.
| | - Sota Tate
- Department of Biochemistry and Molecular Genetics, Ehime University Graduate School of Medicine, Toon, Ehime, 791-0295, Japan; Division of Cell Growth and Tumor Regulation, Proteo-Science Center, Ehime University, Toon, Ehime, 791-0295, Japan
| | - Hiroki Nakaoka
- Department of Dermatology, Ehime University Graduate School of Medicine, Toon, Ehime, 791-0295, Japan
| | - Yasuhiro Fujisawa
- Department of Dermatology, Ehime University Graduate School of Medicine, Toon, Ehime, 791-0295, Japan
| | - Koji Sayama
- Department of Dermatology, Ehime University Graduate School of Medicine, Toon, Ehime, 791-0295, Japan
| | - Shigeki Higashiyama
- Department of Biochemistry and Molecular Genetics, Ehime University Graduate School of Medicine, Toon, Ehime, 791-0295, Japan; Division of Cell Growth and Tumor Regulation, Proteo-Science Center, Ehime University, Toon, Ehime, 791-0295, Japan; Department of Oncogenesis and Tumor Regulation, Osaka International Cancer Institute, Chuo-ku, Osaka, 541-8567, Japan.
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Zhang H. Regulation of DNA Replication Licensing and Re-Replication by Cdt1. Int J Mol Sci 2021; 22:ijms22105195. [PMID: 34068957 PMCID: PMC8155957 DOI: 10.3390/ijms22105195] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Revised: 05/10/2021] [Accepted: 05/12/2021] [Indexed: 11/29/2022] Open
Abstract
In eukaryotic cells, DNA replication licensing is precisely regulated to ensure that the initiation of genomic DNA replication in S phase occurs once and only once for each mitotic cell division. A key regulatory mechanism by which DNA re-replication is suppressed is the S phase-dependent proteolysis of Cdt1, an essential replication protein for licensing DNA replication origins by loading the Mcm2-7 replication helicase for DNA duplication in S phase. Cdt1 degradation is mediated by CRL4Cdt2 ubiquitin E3 ligase, which further requires Cdt1 binding to proliferating cell nuclear antigen (PCNA) through a PIP box domain in Cdt1 during DNA synthesis. Recent studies found that Cdt2, the specific subunit of CRL4Cdt2 ubiquitin E3 ligase that targets Cdt1 for degradation, also contains an evolutionarily conserved PIP box-like domain that mediates the interaction with PCNA. These findings suggest that the initiation and elongation of DNA replication or DNA damage-induced repair synthesis provide a novel mechanism by which Cdt1 and CRL4Cdt2 are both recruited onto the trimeric PCNA clamp encircling the replicating DNA strands to promote the interaction between Cdt1 and CRL4Cdt2. The proximity of PCNA-bound Cdt1 to CRL4Cdt2 facilitates the destruction of Cdt1 in response to DNA damage or after DNA replication initiation to prevent DNA re-replication in the cell cycle. CRL4Cdt2 ubiquitin E3 ligase may also regulate the degradation of other PIP box-containing proteins, such as CDK inhibitor p21 and histone methylase Set8, to regulate DNA replication licensing, cell cycle progression, DNA repair, and genome stability by directly interacting with PCNA during DNA replication and repair synthesis.
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Affiliation(s)
- Hui Zhang
- Department of Chemistry and Biochemistry, Nevada Institute of Personalized Medicine, University of Nevada, Las Vegas, 4505 South Maryland Parkway, Box 454003, Las Vegas, NV 89154, USA
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4
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Lin YC, Prasanth SG. Replication initiation: Implications in genome integrity. DNA Repair (Amst) 2021; 103:103131. [PMID: 33992866 DOI: 10.1016/j.dnarep.2021.103131] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2021] [Revised: 05/07/2021] [Accepted: 05/07/2021] [Indexed: 02/01/2023]
Abstract
In every cell cycle, billions of nucleotides need to be duplicated within hours, with extraordinary precision and accuracy. The molecular mechanism by which cells regulate the replication event is very complicated, and the entire process begins way before the onset of S phase. During the G1 phase of the cell cycle, cells prepare by assembling essential replication factors to establish the pre-replicative complex at origins, sites that dictate where replication would initiate during S phase. During S phase, the replication process is tightly coupled with the DNA repair system to ensure the fidelity of replication. Defects in replication and any error must be recognized by DNA damage response and checkpoint signaling pathways in order to halt the cell cycle before cells are allowed to divide. The coordination of these processes throughout the cell cycle is therefore critical to achieve genomic integrity and prevent diseases. In this review, we focus on the current understanding of how the replication initiation events are regulated to achieve genome stability.
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Chou HC, Bhalla K, Demerdesh OE, Klingbeil O, Hanington K, Aganezov S, Andrews P, Alsudani H, Chang K, Vakoc CR, Schatz MC, McCombie WR, Stillman B. The human origin recognition complex is essential for pre-RC assembly, mitosis, and maintenance of nuclear structure. eLife 2021; 10:61797. [PMID: 33522487 PMCID: PMC7877914 DOI: 10.7554/elife.61797] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Accepted: 01/30/2021] [Indexed: 12/23/2022] Open
Abstract
The origin recognition complex (ORC) cooperates with CDC6, MCM2-7, and CDT1 to form pre-RC complexes at origins of DNA replication. Here, using tiling-sgRNA CRISPR screens, we report that each subunit of ORC and CDC6 is essential in human cells. Using an auxin-inducible degradation system, we created stable cell lines capable of ablating ORC2 rapidly, revealing multiple cell division cycle phenotypes. The primary defects in the absence of ORC2 were cells encountering difficulty in initiating DNA replication or progressing through the cell division cycle due to reduced MCM2-7 loading onto chromatin in G1 phase. The nuclei of ORC2-deficient cells were also large, with decompacted heterochromatin. Some ORC2-deficient cells that completed DNA replication entered into, but never exited mitosis. ORC1 knockout cells also demonstrated extremely slow cell proliferation and abnormal cell and nuclear morphology. Thus, ORC proteins and CDC6 are indispensable for normal cellular proliferation and contribute to nuclear organization.
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Affiliation(s)
- Hsiang-Chen Chou
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States.,Graduate Program in Molecular and Cellular Biology, Stony Brook University, Stony Brook, United States
| | - Kuhulika Bhalla
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| | | | - Olaf Klingbeil
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| | | | - Sergey Aganezov
- Department of Computer Science, Whiting School of Engineering, Johns Hopkins University, Baltimore, United States
| | - Peter Andrews
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| | - Habeeb Alsudani
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| | - Kenneth Chang
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| | | | - Michael C Schatz
- Department of Computer Science, Whiting School of Engineering, Johns Hopkins University, Baltimore, United States
| | | | - Bruce Stillman
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
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Nathanailidou P, Taraviras S, Lygerou Z. DNA Replication Control: Liquid-liquid Phase Separation Comes Into Play. J Mol Biochem 2020; 9:54-56. [PMID: 36532101 PMCID: PMC7613957] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Liquid-liquid phase separation (LLPS) has been recently suggested as a new potential mechanism underpinning various organizational aspects of the cell, from the formation of sub-cellular, biomolecule enrichments to the assembly of organelles. In eukaryotes, DNA replication follows a strict temporal and spatial program that is majorly affected by the chromatin structure, the nuclear organization and the availability of limiting initiation factors; however the regulatory mechanisms driving the process have not been fully elucidated. Original data published lately revealed for the first time that the components of the pre-replicative complex, ORC, Cdc6 and Cdt1, are able to phase separate indicating a possible connection between LLPS and DNA replication. Here, we critically present these preliminary data and propose mechanistic models that could support this regulatory link and lead to new future research directions.
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Affiliation(s)
| | - Stavros Taraviras
- Department of Physiology, School of Medicine, University of Patras, Patras, Greece
| | - Zoi Lygerou
- Department of General Biology, School of Medicine, University of Patras, Patras, Greece
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Abstract
Genetic alterations, including DNA mutations and chromosomal abnormalities, are primary drivers of tumor formation and cancer progression. These alterations can endow cells with a selective growth advantage, enabling cancers to evade cell death, proliferation limits, and immune checkpoints, to metastasize throughout the body. Genetic alterations occur due to failures of the genome stability pathways. In many cancers, the rate of alteration is further accelerated by the deregulation of these processes. The deubiquitinating enzyme ubiquitin specific protease 7 (USP7) has recently emerged as a key regulator of ubiquitination in the genome stability pathways. USP7 is also deregulated in many cancer types, where deviances in USP7 protein levels are correlated with cancer progression. In this work, we review the increasingly evident role of USP7 in maintaining genome stability, the links between USP7 deregulation and cancer progression, as well as the rationale of targeting USP7 in cancer therapy.
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Affiliation(s)
- Gabrielle J Valles
- Department of Molecular Biology and Biophysics, UConn Health, Farmington, CT, United States
| | - Irina Bezsonova
- Department of Molecular Biology and Biophysics, UConn Health, Farmington, CT, United States
| | - Roger Woodgate
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States
| | - Nicholas W Ashton
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States
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Armstrong RL, Penke TJR, Chao SK, Gentile GM, Strahl BD, Matera AG, McKay DJ, Duronio RJ. H3K9 Promotes Under-Replication of Pericentromeric Heterochromatin in Drosophila Salivary Gland Polytene Chromosomes. Genes (Basel) 2019; 10:E93. [PMID: 30700014 DOI: 10.3390/genes10020093] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Revised: 01/24/2019] [Accepted: 01/25/2019] [Indexed: 12/11/2022] Open
Abstract
Chromatin structure and its organization contributes to the proper regulation and timing of DNA replication. Yet, the precise mechanism by which chromatin contributes to DNA replication remains incompletely understood. This is particularly true for cell types that rely on polyploidization as a developmental strategy for growth and high biosynthetic capacity. During Drosophila larval development, cells of the salivary gland undergo endoreplication, repetitive rounds of DNA synthesis without intervening cell division, resulting in ploidy values of ~1350C. S phase of these endocycles displays a reproducible pattern of early and late replicating regions of the genome resulting from the activity of the same replication initiation factors that are used in diploid cells. However, unlike diploid cells, the latest replicating regions of polyploid salivary gland genomes, composed primarily of pericentric heterochromatic enriched in H3K9 methylation, are not replicated each endocycle, resulting in under-replicated domains with reduced ploidy. Here, we employ a histone gene replacement strategy in Drosophila to demonstrate that mutation of a histone residue important for heterochromatin organization and function (H3K9) but not mutation of a histone residue important for euchromatin function (H4K16), disrupts proper endoreplication in Drosophila salivary gland polyploid genomes thereby leading to DNA copy gain in pericentric heterochromatin. These findings reveal that H3K9 is necessary for normal levels of under-replication of pericentric heterochromatin and suggest that under-replication at pericentric heterochromatin is mediated through H3K9 methylation.
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9
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Mughal MJ, Mahadevappa R, Kwok HF. DNA replication licensing proteins: Saints and sinners in cancer. Semin Cancer Biol 2018; 58:11-21. [PMID: 30502375 DOI: 10.1016/j.semcancer.2018.11.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Revised: 11/08/2018] [Accepted: 11/26/2018] [Indexed: 12/12/2022]
Abstract
DNA replication is all-or-none process in the cell, meaning, once the DNA replication begins it proceeds to completion. Hence, to achieve maximum control of DNA replication, eukaryotic cells employ a multi-subunit initiator protein complex known as "pre-replication complex or DNA replication licensing complex (DNA replication LC). This complex involves multiple proteins which are origin-recognition complex family proteins, cell division cycle-6, chromatin licensing and DNA replication factor 1, and minichromosome maintenance family proteins. Higher-expression of DNA replication LC proteins appears to be an early event during development of cancer since it has been a common hallmark observed in a wide variety of cancers such as oesophageal, laryngeal, pulmonary, mammary, colorectal, renal, urothelial etc. However, the exact mechanisms leading to the abnormally high expression of DNA replication LC have not been clearly deciphered. Increased expression of DNA replication LC leads to licensing and/or firing of multiple origins thereby inducing replication stress and genomic instability. Therapeutic approaches where the reduction in the activity of DNA replication LC was achieved either by siRNA or shRNA techniques, have shown increased sensitivity of cancer cell lines towards the anti-cancer drugs such as cisplatin, 5-Fluorouracil, hydroxyurea etc. Thus, the expression level of DNA replication LC within the cell determines a cell's fate thereby creating a paradox where DNA replication LC acts as both "Saint" and "Sinner". With a potential to increase sensitivity to chemotherapy drugs, DNA replication LC proteins have prospective clinical importance in fighting cancer. Hence, in this review, we will shed light on importance of DNA replication LC with an aim to use DNA replication LC in diagnosis and prognosis of cancer in patients as well as possible therapeutic targets for cancer therapy.
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Affiliation(s)
- Muhammad Jameel Mughal
- Cancer Centre, Faculty of Health Sciences, University of Macau, Avenida de Universidade, Taipa, Macau
| | - Ravikiran Mahadevappa
- Cancer Centre, Faculty of Health Sciences, University of Macau, Avenida de Universidade, Taipa, Macau
| | - Hang Fai Kwok
- Cancer Centre, Faculty of Health Sciences, University of Macau, Avenida de Universidade, Taipa, Macau.
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10
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Ramachandran R, Ciaccia PN, Filsuf TA, Jha JK, Chattoraj DK. Chromosome 1 licenses chromosome 2 replication in Vibrio cholerae by doubling the crtS gene dosage. PLoS Genet 2018; 14:e1007426. [PMID: 29795553 PMCID: PMC5991422 DOI: 10.1371/journal.pgen.1007426] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 06/06/2018] [Accepted: 05/17/2018] [Indexed: 12/20/2022] Open
Abstract
Initiation of chromosome replication in bacteria is precisely timed in the cell cycle. Bacteria that harbor multiple chromosomes face the additional challenge of orchestrating replication initiation of different chromosomes. In Vibrio cholerae, the smaller of its two chromosomes, Chr2, initiates replication after Chr1 such that both chromosomes terminate replication synchronously. The delay is due to the dependence of Chr2 initiation on the replication of a site, crtS, on Chr1. The mechanism by which replication of crtS allows Chr2 replication remains unclear. Here, we show that blocking Chr1 replication indeed blocks Chr2 replication, but providing an extra crtS copy in replication-blocked Chr1 permitted Chr2 replication. This demonstrates that unreplicated crtS copies have significant activity, and suggests that a role of replication is to double the copy number of the site that sufficiently increases its activity for licensing Chr2 replication. We further show that crtS activity promotes the Chr2-specific initiator function and that this activity is required in every cell cycle, as would be expected of a cell-cycle regulator. This study reveals how increase of gene dosage through replication can be utilized in a critical regulatory switch.
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Affiliation(s)
- Revathy Ramachandran
- Laboratory of Biochemistry and Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Peter N. Ciaccia
- Laboratory of Biochemistry and Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Tara A. Filsuf
- Laboratory of Biochemistry and Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Jyoti K. Jha
- Laboratory of Biochemistry and Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Dhruba K. Chattoraj
- Laboratory of Biochemistry and Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America
- * E-mail:
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11
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Kang S, Kang MS, Ryu E, Myung K. Eukaryotic DNA replication: Orchestrated action of multi-subunit protein complexes. Mutat Res 2018; 809:58-69. [PMID: 28501329 DOI: 10.1016/j.mrfmmm.2017.04.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Revised: 04/13/2017] [Accepted: 04/30/2017] [Indexed: 06/07/2023]
Abstract
Genome duplication is an essential process to preserve genetic information between generations. The eukaryotic cell cycle is composed of functionally distinct phases: G1, S, G2, and M. One of the key replicative proteins that participate at every stage of DNA replication is the Mcm2-7 complex, a replicative helicase. In the G1 phase, inactive Mcm2-7 complexes are loaded on the replication origins by replication-initiator proteins, ORC and Cdc6. Two kinases, S-CDK and DDK, convert the inactive origin-loaded Mcm2-7 complex to an active helicase, the CMG complex in the S phase. The activated CMG complex begins DNA unwinding and recruits enzymes essential for DNA synthesis to assemble a replisome at the replication fork. After completion of DNA synthesis, the inactive CMG complex on the replicated DNA is removed from chromatin to terminate DNA replication. In this review, we will discuss the structure, function, and regulation of the molecular machines involved in each step of DNA replication.
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Affiliation(s)
- Sukhyun Kang
- Center for Genomic Integrity, Institute for Basic Science, Ulsan 44919, Republic of Korea.
| | - Mi-Sun Kang
- Center for Genomic Integrity, Institute for Basic Science, Ulsan 44919, Republic of Korea
| | - Eunjin Ryu
- Center for Genomic Integrity, Institute for Basic Science, Ulsan 44919, Republic of Korea; School of Life Sciences, Ulsan National Institute for Science and Technology, Ulsan 44919, Republic of Korea
| | - Kyungjae Myung
- Center for Genomic Integrity, Institute for Basic Science, Ulsan 44919, Republic of Korea; School of Life Sciences, Ulsan National Institute for Science and Technology, Ulsan 44919, Republic of Korea
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12
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Abstract
The human tumor viruses that replicate as plasmids (we use the term plasmid to avoid any confusion in the term episome, which was coined to mean DNA elements that occur both extrachromosomally and as integrated forms during their life cycles, as does phage lambda) share many features in their DNA synthesis. We know less about their mechanisms of maintenance in proliferating cells, but these mechanisms must underlie their partitioning to daughter cells. One amazing implication of how these viruses are thought to maintain themselves is that while host chromosomes commit themselves to partitioning in mitosis, these tumor viruses would commit themselves to partitioning before mitosis and probably in S phase shortly after their synthesis.
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