scholarly journals The Oncogenic Small Tumor Antigen of Merkel Cell Polyomavirus Is an Iron-Sulfur Cluster Protein That Enhances Viral DNA Replication

2015 ◽  
Vol 90 (3) ◽  
pp. 1544-1556 ◽  
Author(s):  
Sabrina H. Tsang ◽  
Ranran Wang ◽  
Eiko Nakamaru-Ogiso ◽  
Simon A. B. Knight ◽  
Christopher B. Buck ◽  
...  
Keyword(s):  
Dna Replication ◽  
Viral Replication ◽  
Human Skin ◽  
Merkel Cell Polyomavirus ◽  
Merkel Cell ◽  
Viral Dna ◽  
Direct Role ◽  
Common Component ◽  
Viral Dna Replication ◽  
Iron Sulfur

ABSTRACTMerkel cell polyomavirus (MCPyV) plays an important role in Merkel cell carcinoma (MCC). MCPyV small T (sT) antigen has emerged as the key oncogenic driver in MCC carcinogenesis. It has also been shown to promote MCPyV LT-mediated replication by stabilizing LT. The importance of MCPyV sT led us to investigate sT functions and to identify potential ways to target this protein. We discovered that MCPyV sT purified from bacteria contains iron-sulfur (Fe/S) clusters. Electron paramagnetic resonance analysis showed that MCPyV sT coordinates a [2Fe-2S] and a [4Fe-4S] cluster. We also observed phenotypic conservation of Fe/S coordination in the sTs of other polyomaviruses. Since Fe/S clusters are critical cofactors in many nucleic acid processing enzymes involved in DNA unwinding and polymerization, our results suggested the hypothesis that MCPyV sT might be directly involved in viral replication. Indeed, we demonstrated that MCPyV sT enhances LT-mediated replication in a manner that is independent of its previously reported ability to stabilize LT. MCPyV sT translocates to nuclear foci containing actively replicating viral DNA, supporting a direct role for sT in promoting viral replication. Mutations of Fe/S cluster-coordinating cysteines in MCPyV sT abolish its ability to stimulate viral replication. Moreover, treatment with cidofovir, a potent antiviral agent, robustly inhibits the sT-mediated enhancement of MCPyV replication but has little effect on the basal viral replication driven by LT alone. This finding further indicates that MCPyV sT plays a direct role in stimulating viral DNA replication and introduces cidofovir as a possible drug for controlling MCPyV infection.IMPORTANCEMCPyV is associated with a highly aggressive form of skin cancer in humans. Epidemiological surveys for MCPyV seropositivity and sequencing analyses of healthy human skin suggest that MCPyV may represent a common component of the human skin microbial flora. However, much of the biology of the virus and its oncogenic ability remain to be investigated. In this report, we identify MCPyV sT as a novel Fe/S cluster protein and show that conserved cysteine clusters are important for sT's ability to enhance viral replication. Moreover, we show that sT sensitizes MCPyV replication to cidofovir inhibition. The discovery of Fe/S clusters in MCPyV sT opens new avenues to the study of the structure and functionality of this protein. Moreover, this study supports the notion that sT is a potential drug target for dampening MCPyV infection.

scholarly journals The Ubiquitin-Specific Protease Usp7, a Novel Merkel Cell Polyomavirus Large T-Antigen Interaction Partner, Modulates Viral DNA Replication

2019 ◽  
Vol 94 (5) ◽  
Author(s):  
Manja Czech-Sioli ◽  
Svenja Siebels ◽  
Sonja Radau ◽  
René P. Zahedi ◽  
Claudia Schmidt ◽  
...  
Keyword(s):  
Dna Replication ◽  
Viral Replication ◽  
T Antigen ◽  
Origin Of Replication ◽  
Merkel Cell ◽  
Large T Antigen ◽  
T Antigens ◽  
Viral Dna ◽  
Viral Dna Replication ◽  
Cellular Factors

ABSTRACT Merkel cell polyomavirus (MCPyV) is the major cause for Merkel cell carcinoma (MCC), a rare but highly aggressive skin cancer predominantly found in elderly and immunosuppressed patients. The early viral gene products large T-antigen (LT) and small T-antigen (sT) are important for efficient viral DNA replication, and both contribute to transformation processes. These functions are executed mainly through interactions with host factors. Here, we identify the cellular ubiquitin-specific processing protease 7 (Usp7) as a new interaction partner of the MCPyV LT. Using glutathione S-transferase pulldown experiments, we show that MCPyV LT directly binds to Usp7 and that N- as well as C-terminal regions of LT bind to the TRAF (tumor necrosis factor receptor-associated) domain of Usp7. We demonstrate that endogenous Usp7 coprecipitates with MCPyV T-antigens and relocalizes to viral DNA replication centers in cells actively replicating MCPyV genomes. We show that Usp7 does not alter ubiquitination levels of the T-antigens; however, Usp7 binding increases the binding affinity of LT to the origin of replication, thereby negatively regulating viral DNA replication. Together, these data identify Usp7 as a restriction factor of MCPyV replication. In contrast to other DNA viruses, Usp7 does not affect MCPyV gene expression via its ubiquitination activity but influences MCPyV DNA replication solely via a novel mechanism that modulates binding of LT to viral DNA. IMPORTANCE MCPyV is the only human polyomavirus that is associated with cancer; the majority of Merkel cell cancers have a viral etiology. While much emphasis was placed on investigations to understand the transformation process by MCPyV oncoproteins and cellular factors, we have only limited knowledge of cellular factors participating in the MCPyV life cycle. Here, we describe Usp7, a cellular deubiquitination enzyme, as a new factor involved in MCPyV replication. Usp7 is known in the context of large DNA tumor viruses, Epstein-Barr virus (EBV) and Kaposi’s sarcoma herpesvirus, to restrict viral replication. Similar to EBV, where Usp7 binding to EBNA1 increases EBNA1 binding affinity to viral DNA, we find MCPyV LT binding to the origin of replication to be increased in the presence of Usp7, resulting in restriction of viral DNA replication. However, Usp7-induced restriction of MCPyV replication is independent of its enzymatic activity, thereby constituting a novel mechanism of Usp7-induced restriction of viral replication.

scholarly journals Merkel Cell Polyomavirus DNA Replication Induces Senescence in Human Dermal Fibroblasts in a Kap1/Trim28-Dependent Manner

mBio ◽  
2020 ◽  
Vol 11 (2) ◽  
Author(s):  
Svenja Siebels ◽  
Manja Czech-Sioli ◽  
Michael Spohn ◽  
Claudia Schmidt ◽  
Juliane Theiss ◽  
...  
Keyword(s):  
Gene Expression ◽  
Dna Replication ◽  
Viral Genome ◽  
Cellular Transformation ◽  
Merkel Cell Polyomavirus ◽  
Restriction Factor ◽  
Merkel Cell ◽  
Viral Dna ◽  
Dna Viruses ◽  
Viral Dna Replication

ABSTRACT Merkel cell polyomavirus (MCPyV) is the only polyomavirus known to be associated with tumorigenesis in humans. Similarly to other polyomaviruses, MCPyV expresses a large tumor antigen (LT-Ag) that, together with a small tumor antigen (sT-Ag), contributes to cellular transformation and that is of critical importance for the initiation of the viral DNA replication. Understanding the cellular protein network regulated by MCPyV early proteins will significantly contribute to our understanding of the natural MCPyV life cycle as well as of the mechanisms by which the virus contributes to cellular transformation. We here describe KRAB-associated protein 1 (Kap1), a chromatin remodeling factor involved in cotranscriptional regulation, as a novel protein interaction partner of MCPyV T antigens sT and LT. Kap1 knockout results in a significant increase in the level of viral DNA replication that is highly suggestive of Kap1 being an important host restriction factor during MCPyV infection. Differently from other DNA viruses, MCPyV gene expression is unaffected in the absence of Kap1 and Kap1 does not associate with the viral genome. Instead, we show that in primary normal human dermal fibroblast (nHDF) cells, MCPyV DNA replication, but not T antigen expression alone, induces ataxia telangiectasia mutated (ATM) kinase-dependent Kap1 S824 phosphorylation, a mechanism that typically facilitates repair of double-strand breaks in heterochromatin by arresting the cells in G2. We show that MCPyV-induced inhibition of cell proliferation is mainly conferred by residues within the origin binding domain and thereby by viral DNA replication. Our data suggest that phosphorylation of Kap1 and subsequent Kap1-dependent G2 arrest/senescence represent host defense mechanisms against MCPyV replication in nHDF cells. IMPORTANCE We here describe Kap1 as a restriction factor in MCPyV infection. We report a novel, indirect mechanism by which Kap1 affects MCPyV replication. In contrast with from other DNA viruses, Kap1 does not associate with the viral genome in MCPyV infection and has no impact on viral gene expression. In MCPyV-infected nHDF cells, Kap1 phosphorylation (pKap1 S824) accumulates because of genomic stress mainly induced by viral DNA replication. In contrast, ectopic expression of LT or LT MCPyV mutants, previously shown to be important for induction of genotoxic stress, does not result in a similar extent of pKap1 accumulation. We show that cells actively replicating MCPyV accumulate pKap1 (in a manner dependent on the presence of ATM) and display a senescence phenotype reflected by G2 arrest. These results are supported by transcriptome analyses showing that LT antigen, in a manner dependent on the presence of Kap1, induces expression of secreted factors, which is known as the senescence-associated secretory phenotype (SASP).

scholarly journals Analysis of an Autographa californica Multicapsid Nucleopolyhedrovirus lef-6-Null Virus: LEF-6 Is Not Essential for Viral Replication but Appears To Accelerate Late Gene Transcription

2002 ◽  
Vol 76 (11) ◽  
pp. 5503-5514 ◽  
Author(s):  
Guangyun Lin ◽  
Gary W. Blissard
Keyword(s):  
Dna Replication ◽  
Viral Replication ◽  
Gene Transcription ◽  
Cellular Localization ◽  
Autographa Californica ◽  
Late Gene ◽  
Infection Cycle ◽  
Viral Dna ◽  
Viral Dna Replication ◽  
Late Transcription

ABSTRACT The Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) lef-6 gene was previously shown to be necessary for optimal transcription from an AcMNPV late promoter in transient late expression assays. In the present study, we examined the expression and cellular localization of lef-6 during the AcMNPV infection cycle and generated a lef-6-null virus for studies of the role of lef-6 in the infection cycle. Transcription of lef-6 was detected from 4 to 48 h postinfection, and the LEF-6 protein was identified in dense regions of infected cell nuclei, a finding consistent with its potential role as a late transcription factor. To examine lef-6 in the context of the AcMNPV infection cycle, we deleted the lef-6 gene from an AcMNPV genome propagated as an infectious BACmid in Escherichia coli. Unexpectedly, the resulting AcMNPV lef-6-null BACmid (vAclef6KO) was able to propagate in cell culture, although virus yields were substantially reduced. Thus, the lef-6 gene is not essential for viral replication in Sf9 cells. Two “repair” AcMNPV BACmids (vAclef6KO-REP-P and vAclef6KO-REP-ie1P) were generated by transposition of the lef-6 gene into the polyhedrin locus of the vAclef6KO BACmid. Virus yields from the two repair viruses were similar to those from wild-type AcMNPV or a control (BACmid-derived) virus. The lef-6-null BACmid (vAclef6KO) was further examined to determine whether the deletion of lef-6 affected DNA replication or late gene transcription in the context of an infection. The lef-6 deletion did not appear to affect viral DNA replication. Using Northern blot analysis, we found that although early transcription was apparently unaffected, both late and very late transcription were delayed in cells infected with the lef-6-null BACmid. This phenotype was rescued in viruses containing the lef-6 gene reinserted into the polyhedrin locus. Thus, the lef-6 gene was not essential for either viral DNA replication or late gene transcription, but the absence of lef-6 resulted in a substantial delay in the onset of late transcription. Therefore, lef-6 appears to accelerate the infection cycle of AcMNPV.

scholarly journals Analysis of an Autographa californica Nucleopolyhedrovirus lef-11 Knockout: LEF-11 Is Essential for Viral DNA Replication

2002 ◽  
Vol 76 (6) ◽  
pp. 2770-2779 ◽  
Author(s):  
Guangyun Lin ◽  
Gary W. Blissard
Keyword(s):  
Dna Replication ◽  
Viral Replication ◽  
Autographa Californica ◽  
Sf9 Cells ◽  
Infection Cycle ◽  
Wild Type ◽  
Viral Dna ◽  
Viral Dna Replication ◽  
Late Transcription ◽  
Late Expression

ABSTRACT The Autographa californica nucleopolyhedrovirus (AcMNPV) lef-11 gene was previously identified by transient late expression assays as a gene important for viral late gene expression. The lef-11 gene was not previously identified as necessary for DNA replication in transient origin-dependent plasmid DNA replication assays. To examine the role of lef-11 in the context of the infection cycle, we generated a deletion of the lef-11 gene by recombination in an AcMNPV genome propagated as a BACmid in Escherichia coli. The resulting AcMNPV lef-11-null BACmid (vAclef11KO) was unable to propagate in cell culture, although a “repair” AcMNPV BACmid (vAclef11KO-REP), which was generated by transposition of the lef-11 gene into the polyhedrin locus of the vAclef11KO BACmid, was able to replicate in a manner similar to wild-type or control AcMNPV viruses. Thus, the lef-11 gene is essential for viral replication in Sf9 cells. The vAclef11KO BACmid was examined to determine if the defect in viral replication resulted from a defect in DNA replication or from a defect in late transcription. The lef-11-null BACmid and control BACmids were transfected into Sf9 cells, and viral DNA replication was monitored. The viral DNA genome of the lef-11-null BACmid (vAclef11KO) was not amplified, whereas replication and amplification of the genomes of the repair BACmid (vAclef11KO-REP), wild-type AcMNPV, and a nonpropagating gp64-null control BACmid (vAcGUSgp64KO) were readily detected. Northern blot analysis of transcripts from selected early, late, and very late genes showed that late and very late transcription was absent in cells transfected with the lef-11-null BACmid. Thus, in contrast to prior studies using transient replication and late expression assays, studies of a lef-11-null BACmid indicate that LEF-11 is required for viral DNA replication during the infection cycle.

scholarly journals The Human Cytomegalovirus IE2 and UL112-113 Proteins Accumulate in Viral DNA Replication Compartments That Initiate from the Periphery of Promyelocytic Leukemia Protein-Associated Nuclear Bodies (PODs or ND10)

1999 ◽  
Vol 73 (12) ◽  
pp. 10458-10471 ◽  
Author(s):  
Jin-Hyun Ahn ◽  
Won-Jong Jang ◽  
Gary S. Hayward
Keyword(s):  
Dna Replication ◽  
Viral Replication ◽  
Human Cytomegalovirus ◽  
Promyelocytic Leukemia ◽  
Nuclear Bodies ◽  
Viral Dna ◽  
Viral Dna Replication ◽  
Promyelocytic Leukemia Protein ◽  
The Core ◽  
Replication Compartment

ABSTRACT During human cytomegalovirus (HCMV) infection, the periphery of promyelocytic leukemia protein (PML)-associated nuclear bodies (also known as PML oncogenic domains [PODs] or ND10) are sites for both input viral genome deposition and immediate-early (IE) gene transcription. At very early times after infection, the IE1 protein localizes to and subsequently disrupts PODs, whereas the IE2 protein localizes within or adjacent to PODs. This process appears to be required for efficient viral gene expression and DNA replication. We have investigated the initiation of viral DNA replication compartment formation by studying the localization of viral IE proteins, DNA replication proteins, and the PML protein during productive infection. Localization of IE2 adjacent to PODs between 2 and 6 h after infection was confirmed by confocal microscopy of human fibroblasts (HF cells) infected with both wild-type HCMV(Towne) and with an IE1-deletion mutant HCMV(CR208) that fails to disrupt PODs. In HCMV(Towne)-infected HF cells at 24 to 48 h, IE2 also accumulated in newly formed viral DNA replication compartments containing the polymerase processivity factor (UL44), the single-stranded DNA binding protein (SSB; UL57), the UL112-113 accessory protein, and newly incorporated bromodeoxyuridine (BrdU). Double labeling of the HCMV(CR208)-infected HF cells demonstrated that formation of viral DNA replication compartments initiates within granular structures that bud from the periphery of some of the PODs and subsequently coalesce into larger structures that are flanked by PODs. In transient DNA transfection assays, both the N terminus (codons 136 to 290) and the C terminus (codons 379 to 579) of IE2 exon 5, but not the central region between them, were found to be necessary for both the punctate distribution of IE2 and its association with PODs. Like IE2, the UL112-113 accessory replication protein was also distributed in a POD-associated pattern in both DNA-transfected and virus-infected cells beginning at 6 h. Furthermore, when all six replication core machinery proteins (polymerase complex, SSB, and helicase-primase complex) were expressed together in the presence of UL112-113, they also accumulated at POD-associated sites, suggesting that the UL112-113 protein (but not IE2) may play a role in recruitment of viral replication fork proteins into the periphery of PODs. These results show that (i) subsequent to accumulating at the periphery of PODs, IE2 is incorporated together with the core proteins into viral DNA replication compartments that initiate from the periphery of PODs and then grow to fill the space between groups of PODs, and (ii) the UL112-113 protein appears to have a key role in assembling and recruiting the core replication machinery proteins in the initial stages of viral replication compartment formation.

scholarly journals Antiviral Properties of the LSD1 Inhibitor SP-2509

2020 ◽  
Vol 94 (19) ◽  
Author(s):  
Mitchell R. Harancher ◽  
Jessica E. Packard ◽  
Shane P. Cowan ◽  
Neal A. DeLuca ◽  
Jill A. Dembowski
Keyword(s):  
Gene Expression ◽  
Life Cycle ◽  
Dna Replication ◽  
Viral Replication ◽  
Virus Production ◽  
Coupled Processes ◽  
Viral Dna ◽  
Viral Dna Replication ◽  
Pol Ii ◽  
Hsv 1

ABSTRACT Lysine-specific demethylase 1 (LSD1) targets cellular proteins, including histone H3, p53, E2F, and Dnmt1, and is involved in the regulation of gene expression, DNA replication, the cell cycle, and the DNA damage response. LSD1 catalyzes demethylation of histone H3K9 associated with herpes simplex virus 1 (HSV-1) immediate early (IE) promoters and is necessary for IE gene expression, viral DNA replication, and reactivation from latency. We previously found that LSD1 associates with HSV-1 replication forks and replicating viral DNA, suggesting that it may play a direct role in viral replication or coupled processes. We investigated the effects of the LSD1 inhibitor SP-2509 on the HSV-1 life cycle. Unlike previously investigated LSD1 inhibitors tranylcypromine (TCP) and OG-L002, which covalently attach to the LSD1 cofactor flavin adenine dinucleotide (FAD) to inhibit demethylase activity, SP-2509 has previously been shown to inhibit LSD1 protein-protein interactions. We found that SP-2509 does not inhibit HSV-1 IE gene expression or transcription factor and RNA polymerase II (Pol II) association with viral DNA prior to the onset of replication. However, SP-2509 does inhibit viral DNA replication, late gene expression, and virus production. We used EdC labeling of nascent viral DNA to image aberrant viral replication compartments that form in the presence of SP-2509. Treatment resulted in the formation of small replication foci that colocalize with replication proteins but are defective for Pol II recruitment. Taken together, these data highlight a potential new role for LSD1 in the regulation of HSV-1 DNA replication and gene expression after the onset of DNA replication. IMPORTANCE Treatment of HSV-1-infected cells with SP-2509 blocked viral DNA replication, gene expression after the onset of DNA replication, and virus production. These data support a potential new role for LSD1 in the regulation of viral DNA replication and successive steps in the virus life cycle, and further highlight the promising potential to utilize LSD1 inhibition as an antiviral approach.

scholarly journals Host AAA+ ATPase TER94 Plays Critical Roles in Building the Baculovirus Viral Replication Factory and Virion Morphogenesis

2020 ◽  
Vol 94 (6) ◽  
Author(s):  
Yimeng Li ◽  
Liangbo Hu ◽  
Tong Chen ◽  
Meng Chang ◽  
Fei Deng ◽  
...  
Keyword(s):  
Life Cycle ◽  
Dna Replication ◽  
Viral Replication ◽  
Protein Quality ◽  
Viral Dna ◽  
Viral Dna Replication ◽  
Aaa Atpase ◽  
Cellular Processes ◽  
Early Proteins ◽  
Virion Morphogenesis

ABSTRACT TER94 is a multifunctional AAA+ ATPase crucial for diverse cellular processes, especially protein quality control and chromatin dynamics in eukaryotic organisms. Many viruses, including coronavirus, herpesvirus, and retrovirus, coopt host cellular TER94 for optimal viral invasion and replication. Previous proteomics analysis identified the association of TER94 with the budded virions (BVs) of baculovirus, an enveloped insect large DNA virus. Here, the role of TER94 in the prototypic baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) life cycle was investigated. In virus-infected cells, TER94 accumulated in virogenic stroma (VS) at the early stage of infection and subsequently partially rearranged in the ring zone region. In the virions, TER94 was associated with the nucleocapsids of both BV and occlusion-derived virus (ODV). Inhibition of TER94 ATPase activity significantly reduced viral DNA replication and BV production. Electron/immunoelectron microscopy revealed that inhibition of TER94 resulted in the trapping of nucleocapsids within cytoplasmic vacuoles at the nuclear periphery for BV formation and blockage of ODV envelopment at a premature stage within infected nuclei, which appeared highly consistent with its pivotal function in membrane biogenesis. Further analyses showed that TER94 was recruited to the VS or subnuclear structures through interaction with viral early proteins LEF3 and helicase, whereas inhibition of TER94 activity blocked the proper localization of replication-related viral proteins and morphogenesis of VS, providing an explanation for its role in viral DNA replication. Taken together, these data indicated the crucial functions of TER94 at multiple steps of the baculovirus life cycle, including genome replication, BV formation, and ODV morphogenesis. IMPORTANCE TER94 constitutes an important AAA+ ATPase that associates with diverse cellular processes, including protein quality control, membrane fusion of the Golgi apparatus and endoplasmic reticulum network, nuclear envelope reformation, and DNA replication. To date, little is known regarding the role(s) of TER94 in the baculovirus life cycle. In this study, TER94 was found to play a crucial role in multiple steps of baculovirus infection, including viral DNA replication and BV and ODV formation. Further evidence showed that the membrane fission/fusion function of TER94 is likely to be exploited by baculovirus for virion morphogenesis. Moreover, TER94 could interact with the viral early proteins LEF3 and helicase to transport and further recruit viral replication-related proteins to establish viral replication factories. This study highlights the critical roles of TER94 as an energy-supplying chaperon in the baculovirus life cycle and enriches our knowledge regarding the biological function of this important host factor.

scholarly journals Kaposi's Sarcoma-Associated Herpesvirus mRNA Accumulation in Nuclear Foci Is Influenced by Viral DNA Replication and Viral Noncoding Polyadenylated Nuclear RNA

2018 ◽  
Vol 92 (13) ◽  
Author(s):  
Tenaya K. Vallery ◽  
Johanna B. Withers ◽  
Joana A. Andoh ◽  
Joan A. Steitz
Keyword(s):  
Dna Replication ◽  
Viral Replication ◽  
Dna Synthesis ◽  
Host Cell ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Viral Dna ◽  
Viral Dna Replication ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACTKaposi's sarcoma-associated herpesvirus (KSHV), like other herpesviruses, replicates within the nuclei of its human cell host and hijacks host machinery for expression of its genes. The activities that culminate in viral DNA synthesis and assembly of viral proteins into capsids physically concentrate in nuclear areas termed viral replication compartments. We sought to better understand the spatiotemporal regulation of viral RNAs during the KSHV lytic phase by examining and quantifying the subcellular localization of select viral transcripts. We found that viral mRNAs, as expected, localized to the cytoplasm throughout the lytic phase. However, dependent on active viral DNA replication, viral transcripts also accumulated in the nucleus, often in foci in and around replication compartments, independent of the host shutoff effect. Our data point to involvement of the viral long noncoding polyadenylated nuclear (PAN) RNA in the localization of an early, intronless viral mRNA encoding ORF59-58 to nuclear foci that are associated with replication compartments.IMPORTANCELate in the lytic phase, mRNAs from Kaposi's sarcoma-associated herpesvirus accumulate in the host cell nucleus near viral replication compartments, centers of viral DNA synthesis and virion production. This work contributes spatiotemporal data on herpesviral mRNAs within the lytic host cell and suggests a mechanism for viral RNA accumulation. Our findings indicate that the mechanism is independent of the host shutoff effect and splicing but dependent on active viral DNA synthesis and in part on the viral noncoding RNA, PAN RNA. PAN RNA is essential for the viral life cycle, and its contribution to the nuclear accumulation of viral messages may facilitate propagation of the virus.

scholarly journals Herpes simplex virus 1 ICP8 mutant lacking annealing activity is deficient for viral DNA replication

2018 ◽  
Vol 116 (3) ◽  
pp. 1033-1042 ◽  
Author(s):  
Savithri Weerasooriya ◽  
Katherine A. DiScipio ◽  
Anthar S. Darwish ◽  
Ping Bai ◽  
Sandra K. Weller
Keyword(s):  
Herpes Simplex Virus ◽  
Dna Replication ◽  
Herpes Simplex ◽  
Viral Replication ◽  
Single Strand ◽  
Replication Proteins ◽  
Viral Dna ◽  
Viral Dna Replication ◽  
Simplex Virus

Most DNA viruses that use recombination-dependent mechanisms to replicate their DNA encode a single-strand annealing protein (SSAP). The herpes simplex virus (HSV) single-strand DNA binding protein (SSB), ICP8, is the central player in all stages of DNA replication. ICP8 is a classical replicative SSB and interacts physically and/or functionally with the other viral replication proteins. Additionally, ICP8 can promote efficient annealing of complementary ssDNA and is thus considered to be a member of the SSAP family. The role of annealing during HSV infection has been difficult to assess in part, because it has not been possible to distinguish between the role of ICP8 as an SSAP from its role as a replicative SSB during viral replication. In this paper, we have characterized an ICP8 mutant, Q706A/F707A (QF), that lacks annealing activity but retains many other functions characteristic of replicative SSBs. Like WT ICP8, the QF mutant protein forms filaments in vitro, binds ssDNA cooperatively, and stimulates the activities of other replication proteins including the viral polymerase, helicase–primase complex, and the origin binding protein. Interestingly, the QF mutant does not complement an ICP8-null virus for viral growth, replication compartment formation, or DNA replication. Thus, we have been able to separate the activities of ICP8 as a replicative SSB from its annealing activity. Taken together, our data indicate that the annealing activity of ICP8 is essential for viral DNA replication in the context of infection and support the notion that HSV-1 uses recombination-dependent mechanisms during DNA replication.

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