DNA replication of human cytomegalovirus (HCMV) is a highly regulated process that requires specific interactions between cis-acting lytic origin of replication (oriLyt) and trans-acting viral proteins. Formation of the replication initiation complex is also regulated by specific interactions among viral replication proteins. HCMV replication proteins include origin-binding proteins, core proteins that work in replication forks, and regulatory proteins that modulate host cell functions. This letter describes intriguing questions regarding how HCMV origin-binding proteins interact with oriLyt to initiate DNA replication and how the regulatory UL112-113 proteins, which are found only in beta-herpesviruses, function to promote viral DNA replication.
Cytomegalovirus ; DNA ; DNA Replication ; DNA, Viral ; Humans ; Proteins ; Replication Origin ; Viral Proteins

Topoisomerases are nuclear enzymes that regulate the overwinding or underwinding of DNA helix during replication, transcription, recombination, repair, and chromatin remodeling. These enzymes perform topological transformations by providing a transient DNA break, through which the unique problems of DNA entanglement that occur owing to unwinding and rewinding of the DNA helix can be resolved. In mammals, topoisomerases are classified into two types, type I topoisomerase (Top1) and type II topoisomerase (Top2), depending on the number of strands cut in one round of action. Top1 induces single-strand breaks in DNA, and Top2 induces double-strand breaks. In cells from vertebrate species, there are two forms of Top2, designated alpha and beta. Top2α is involved in the cellular proliferation and pluripotency, while Top2β plays key roles in neurodevelopment. In this review, we cover recent advances in structural, mechanistic and functional insights into Top2.
Animals ; Cell Proliferation ; DNA Replication ; DNA Topoisomerases, Type II ; chemistry

Real-time quantitative PCR was used to characterize HearNPV DNA replication in exponential and stationary phases of HzAM1 cells. Results showed that the doubling time of HzAM1 cells was 22 h in exponential phases. Most of the exponential cells were in S phase (48.6%), and most of the stationary cells in G2/M phase (72.6%). The replication of viral DNA was completed within 60 h post infection (h p. i.) in different phases of HzAM1 cells. During 14 to 20 h p. i., the doubling time of HearNPV replica-tion was 1.8 h in exponential cells and 1.9 h in stationary cells, and no significant difference was found between them. But the amounts of BV entering and releasing, the final progeny virions and viral protein products in the infected exponential phase cells were obviously higher than that in the stationary phase cells. 25% of the total synthesized viral DNAs were released from infected exponential phase cells, but on-ly 13% from the infected stationary phase cells. Viral DNA started to be replicated from 7-8 h p. i. both in infected exponential phase and in stationary phase cells. But in infected exponential phase cells, BVs were started to release from 18-20 h p. i., and BVs were started to release from 22-25 h p. i. from infected sta-tionary phase cells. During 30-60 h p. i., the BV releasing rate was about 483 copies/cell/h in the expo-nential phase cells, but was 100 copies/cell/h in the stationary-phase cells. The initial viral DNA entering into exponential phase cells was much more than that entered into the stationary phase cells. The data of cell membrane fluidity at exponential and stationary phases suggested that the fluidity of cell membrane played an important role during virus entry.
Animals ; Cell Cycle ; Cell Line ; DNA Replication ; Membrane Fluidity ; Moths ; Nucleopolyhedrovirus ; physiology ; Virus Internalization ; Virus Replication

DNA Replication ; Epigenesis, Genetic ; Hepatitis B virus ; genetics ; physiology ; Virus Replication

OBJECTIVETo investigate the effect of HS3ST3B1 on hepatitis B virus (HBV) replication.

METHODSHepG2 cells were classified into 7 groups according to the plasmids transfected: (1) Blank group, no plasmid transfected; 2. Positive control, transfected with pCH9-HBV which permits HBV replication; (3) Negative control, transfected with pCH9-HBV + pcDNA3.1 + pTZU6+1; (4) Treatment A, transfected with pCH9-HBV + pCDNA3.1-HS3ST3B1 + pTZU6+1; (5) Interference A, transfected with pCH9-HBV + pCDNA3.1-HS3ST3B1 + psh1126 (a plasmid to interfere HS3ST3B1 expression); (6) Treatment B, transfected with pCH9-HBV + pTZU6+1; (7) Interference B, transfected with pCH9-HBV + psh1126. The levels of HBV DNA were detected in the above groups by Southern blotting. HBV total RNA of Negative control, Treatment A and Interference A were quantified by Real-time PCR to determine the influence of HS3ST3B1 over-expression on the HBV RNA transcription. The activity of the four HBV promoters [core promoter (cp), x promoter(xp), surface antigen promoter1(sp1), surface antigen promoter2 (sp2)] were assayed by Dual-Luciferase Reporter Assay System. The data was analyzed using one way ANOVA, with P < 0.05 indicating statistically meaningful difference.

RESULTSouthern blot data revealed the level of HBV DNA in Treatment A and Interference A accounted for 10% +/- 2% and 31% +/- 4% of that in control. Compared with control, a statistical difference existed between Treatment A and Control, with F value equalling to 20.8 and P value equalling to 0.034 respectively. A statistical difference also existed between Interfere A and Treatment A, with F value equalling to 24.9 and P value equalling to 0.021 respectively. The level of HBV DNA in Experiment B was raised by 130% +/- 11% as compared to that in Interference B, and the levels of HBV DNA showed a dose-dependent decrease when H7 cells were transfected with 0.5, 1.0, 1.5 microg pCDNA3.1-HS3ST3B1 respectively. Statistical differences existed between control and H7 transfected with different dose of pCDNA3.1-HS3ST3B1, with F values equalling to 22.7, 20.3, 26.5 and P values equalling to 0.029, 0.041 and 0.015 respectively. Real-time PCR revealed that the HBV total RNA in Treatment A accounted for 17.0% +/- 2.7% of that in control and there was a statistical difference between Treatment A and control, with F value equalling to 25.6 and P value equalling to 0.018. In addition, HBV DNA in Interference A was restored to 74.0% +/- 3.9% of that in control, and there was also a statistical difference between Treatment A and Interference A, with F value equalling to 21.3 and P value equalling to 0.032. However, the down regulation of HBV total RNA had nothing to do with HBV promoters activity.

CONCLUSIONHS3ST3B1 can inhibit HBV replication and reduce the level of HBV total RNA, but the downregulation of HBV total RNA may not be the result of direct interaction of HS3ST3B1 and HBV promoters.

DNA Replication ; DNA, Viral ; biosynthesis ; Hep G2 Cells ; Hepatitis B virus ; genetics ; physiology ; Humans ; Plasmids ; Sulfotransferases ; genetics ; Transfection ; Virus Replication

Genetic instability is considered to be a major driving force of malignancy of cancer cells, and at least some of cancer-associated genetic instability is known to be caused by defects in the cell cycle checkpoint control. Patients of the cancer-prone genetic disorder ataxia telangiectagia frequently develop malignant lymphoma and their cells are defective in gamma-irradiation responsive checkpoint control, whereas cells inactivated for the p53 recessive oncoprotein are defective in DNA damage-induced checkpoint control and develop genetic instability. Cells contain two major cell cycle checkpoint control systems: DNA-replication checkpoint, DNA-damage checkpoint. These checkpoint systems are thought to consist of three functionally distinct components: sensors, checkpoint signal transducers and cell cycle effecters. Recent rapid progress in the identification of these components is beginning to prove this conceptual model and the generality of the checkpoint system among eukaryotes. The full understanding of the cell cycle checkpoint control system will provide deeper insights into the highly complex mechanisms of carcinogenesis and highlight possible targets for cancer therapy.
Ataxia ; Carcinogenesis ; Cell Cycle Checkpoints* ; Cell Cycle* ; DNA ; DNA Damage ; DNA Replication ; Eukaryota ; Humans ; Lymphoma ; Transducers

Besides single-nucleotide variants in the human genome, large-scale genomic variants, such as copy number variations (CNVs), are being increasingly discovered as a genetic source of human diversity and the pathogenic factors of diseases. Recent experimental findings have shed light on the links between different genome architectures and CNV mutagenesis. In this review, we summarize various genomic features and discuss their contributions to CNV formation. Genomic repeats, including both low-copy and high-copy repeats, play important roles in CNV instability, which was initially known as DNA recombination events. Furthermore, it has been found that human genomic repeats can also induce DNA replication errors and consequently result in CNV mutations. Some recent studies showed that DNA replication timing, which reflects the high-order information of genomic organization, is involved in human CNV mutations. Our review highlights that genome architecture, from DNA sequence to high-order genomic organization, is an important molecular factor in CNV mutagenesis and human genomic instability.
Base Sequence ; DNA ; DNA Copy Number Variations ; DNA Replication ; DNA Replication Timing ; Genome* ; Genome, Human ; Genomic Instability ; Humans ; Mutagenesis ; Recombination, Genetic

To investigate fragile sites induced by aphidicolin which is a specific inhibitor of eukaryotic DNA polymerase a which is primarily associated with chromosomal DNA replication in human lymphocytes, HaCat cells (human keratinocytes) and MRC-5 cells (human embryonic lung fibroblast), we cultured each cells in RPMI 1640 with 10% fetal calf serum and 2% PHA. Treatment of the cells with aphidicolin was generally carried out for the last 24 hours of culturing. The drug was dissolved in DMSO and used at final concentrations of 0.05~0.15 mg/ml, corresponding to a maximum DMSO concentration of 0.028%. Karyotypes of each cells were performed by routine method, and 50 metaphases were scored for each culture for analysis of breakage rate. Experimental cells treated with APC showed a dose dependent sensitivity and the amounts of chromosome breakage induced by APC are the highest in concentration of 0.15 mg/ml. The frequency of fragile sites on each cells appeared in MRC-5 cells, lymphocytes and HaCat cells in order. The common fragile sites on all experiments was 16q23, and the common fragile sites on embryonic cells was 1p31. It can be concluded that gene or nucleic acid which is located on 16q23 is the most important factor to induce chromosomal breakage with sensitivity to aphidicolin and 1p31 is important site to induce chromosomal breakage in embryonal cells.
Aphidicolin* ; Chromosome Breakage ; Dimethyl Sulfoxide ; DNA ; DNA Replication ; Humans ; Karyotype ; Lung ; Lymphocytes* ; Metaphase

OBJECTIVE: To study the correlation of Mycoplasma pneumoniae DNA (MP-DNA) replication level in throat swab and bronchoalveolar lavage fluid (BALF) with disease severity in children with severe Mycoplasma pneumoniae pneumonia (SMPP). METHODS: A total of 44 children with SMPP who underwent bronchoalveolar lavage were enrolled as subjects. The serum levels of cytokines and MP-DNA replication times in throat swab were measured in the acute stage and the recovery stage, and the levels of interleukin (IL)-8 and MP-DNA replication times in BALF were measured in the acute stage. According to whether mechanical ventilation was needed for respiratory failure, the children were divided into a mechanical ventilation group (n=19) and a non-mechanical ventilation group (n=25), and the two groups were compared in MP-DNA replication times in BALF. RESULTS: For the children with SMPP, serum levels of C-reactive protein, erythrocyte sedimentation rate, lactate dehydrogenase, IL-1, IL-6, IL-8, and IL-18 in the acute stage were significantly higher than those in the recovery stage (P<0.05). In the acute stage, MP-DNA replication times in throat swab were positively correlated with those in BALF (r=0.613, P<0.05), and MP-DNA replication times in BALF were positively correlated with IL-18 levels in peripheral blood and BALF (r=0.613 and 0.41 respectively, P<0.05). Compared with the non-mechanical ventilation group, the mechanical ventilation group had significantly higher MP-DNA replication times in BALF, a significantly longer duration of systemic hormone treatment, significantly higher serum levels of lactate dehydrogenase and IL-18, and significantly higher white blood cell count and IL-18 level in BALF (P<0.05). CONCLUSIONS In children with SMPP, MP-DNA replication level in throat swab and BALF can be used as a reference index for the assessment of disease severity.
Bronchoalveolar Lavage Fluid ; Child ; Cytokines ; DNA Replication ; DNA, Bacterial ; Humans ; Mycoplasma pneumoniae ; Pneumonia, Mycoplasma

To explore the molecular mechanism of human papillomavirus subtype 16(HPV-16)E7 oncogene-induced DNA re-replication in response to DNA damage. Flow cytometry was performed to examine the cell cycle changes in RPE1 E7 cells stably expressing HPV-16 E7 and its control cell RPE1 Vector after DNA damage.Immunoblotting assay was used to evaluate the early mitotic inhibitor 1(Emi1)expression in RPE1 E7 and RPE1 Vector cells with or without DNA damage.The changes of the proportion of polyploidy was detected by flow cytometry in DNA-damaged RPE1 E7 cells interfered by Emi1 small interfering RNA. Compared with the control cells,the proportion of polyploids in RPE1 E7 cells was significantly increased in response to DNA damage(=6.397,=0.0031).Emi1 protein expression was significantly increased in DNA damaged RPE1 E7 cells(=8.241,=0.0012).The polyploid ratio of RPE1 E7 cells was significantly reduced after Emi1 was interfered by two independent small interfering RNAs(=2.916,=0.0434;=3.452,=0.0260). In response to DNA damage,Emi1 promoted DNA re-replication caused by HPV-16 E7.
DNA Damage ; DNA Replication ; Human papillomavirus 16 ; Mitosis ; Oncogene Proteins, Viral