Replication of Herpes Simplex Virus DNA (1999)

Herpes simplex virus type 1 (HSV-1) 1The abbreviations used are:HSV-1herpes simplex virus type 1bpbase pairs is a member of the herpes group of viruses, the Herpesviridiae, which includes the important human pathogens herpes simplex virus type 2, cytomegalovirus, varicella zoster virus, Epstein-Barr virus, human herpesviruses 6 and 7, and Kaposi's associated herpesvirus, human herpesvirus 8 (reviewed in Ref. 1Roizman B. Sears A.E. Fields B.N. Knipe D.M. Howley P.M. Fields Virology. Lippincott-Raven, Philadelphia, PA1996: 2231-2295Google Scholar). Of these, HSV-1 has been the most extensively studied. The HSV-1 genome is a 153-kilobase linear duplex with 75 open reading frames. It consists of two unique regions, UL (unique long), comprising 82% and the US(unique short) comprising 18%, flanked by the repeated regionsa, b, and c (Fig.1). As a consequence of recombination through the a sequences, the HSV-1 genome actually exists as an equimolar mixture of four isomeric forms generated by inversion of the UL and US sequences relative to each other. herpes simplex virus type 1 base pairs An interesting but poorly understood aspect of the HSV-1 life cycle, in fact, the life cycle of all the herpesviruses, is the ability to enter latency, a state in which no infectious progeny are produced and only limited transcription of viral genes occurs. Upon presentation of the appropriate stimulus, the latently infected cells enter a lytic phase with the resultant production of infectious viral particles (1Roizman B. Sears A.E. Fields B.N. Knipe D.M. Howley P.M. Fields Virology. Lippincott-Raven, Philadelphia, PA1996: 2231-2295Google Scholar). In the lytic phase, following penetration of the nucleus, a temporally regulated program of viral gene expression mediated by RNA polymerase II begins. A virion protein, VP16, acts in trans together with the cellular octamer DNA-binding protein, Oct-1, to induce the α or immediate early genes, the first set of HSV-1 genes to be expressed. These serve as transactivators of β or earlygene expression. Their synthesis peaks at 2–4 h, postinfection. Functional α proteins are required for the synthesis of all the virally encoded proteins. Synthesis of the β class of proteins reaches peak rates 5–7 h and is detectable as early as 3 h postinfection. The β proteins include the enzymes that are required for replication of the viral genome: a DNA polymerase, a single-strand DNA-binding protein, a primosome or helicase-primase, an origin-binding protein, and a set of enzymes involved in DNA repair and in deoxynucleotide metabolism. Homologues of these proteins are found in virtually all herpesviruses (1Roizman B. Sears A.E. Fields B.N. Knipe D.M. Howley P.M. Fields Virology. Lippincott-Raven, Philadelphia, PA1996: 2231-2295Google Scholar, 2Boehmer P.E. Lehman I.R. Annu. Rev. Biochem. 1997; 66: 347-384Crossref PubMed Scopus (268) Google Scholar). Viral DNA synthesis begins shortly after the appearance of the β proteins and is detectable as early as 3 h and continues up to 15 h postinfection, with the bulk of the DNA synthesized during the latter part of the period. The temporal program of viral gene expression ends with the appearance of the γ or lateproteins, which constitute the structural proteins of the virus (1Roizman B. Sears A.E. Fields B.N. Knipe D.M. Howley P.M. Fields Virology. Lippincott-Raven, Philadelphia, PA1996: 2231-2295Google Scholar). As early as 0.5 h postinfection and in the absence of protein synthesis, viral DNA accumulates in the nucleus and adopts an "endless" configuration whose structure is consistent with circularization (1Roizman B. Sears A.E. Fields B.N. Knipe D.M. Howley P.M. Fields Virology. Lippincott-Raven, Philadelphia, PA1996: 2231-2295Google Scholar). Although the mechanism of genome circularization has not been established, it may involve a recombination event through the terminal repeat sequences. One clear advantage of this intermediate is that it eliminates the need for a specialized mechanism to replicate the termini. Although there is no firm proof for the existence of thetareplication intermediates that initiate at one or more of the HSV-1 origins in vivo, genome circularization is a prerequisite for viral replication, and replication requires either oriSor oriL and the action of a viral protein that possesses all the properties of an initiator protein (UL9 protein). These observations strongly suggest that HSV-1 DNA replication initiates by atheta mechanism and make it unlikely that other mechanisms, such as inter- or intramolecular recombination or transcription, all of which could potentially occur on linear DNA templates, are responsible for the initiation of HSV-1 DNA replication. At some point and by an as yet undefined mechanism, theta replication switches to the rolling circle mode, the predominant mode of HSV-1 DNA replication. In the rolling circle mode, DNA replication generates long head-to-tail concatamers similar to the DNA replication products observed during the theta phase of bacteriophage λ replication (3Stahl F.W. Stahl M.M. Hershey A.D. The Bacteriophage Lambda. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY1971: 195-210Google Scholar). At late times during viral DNA replication, the products consist of branched networks of concatamers that may arise from recombination and invading DNA replication forks. The HSV-1 genome contains three cis-acting elements, which function as origins of DNA replication: one copy of oriL, located between the diverging UL29 andUL30 genes within UL, and two copies of oriS, located within the c sequences (Fig.2). Both oriS and oriL contain large palindromes of 45 and 144 bp, respectively, that center around an A + T region of 18 and 20 bp, respectively. Flanking the A + T region are inverted repeats that are binding sites for the HSV-1-encoded origin-binding protein (UL9 protein). It is unclear why the HSV-1 genome contains multiple origins that appear identical in every respect other than size and location. The existence of two copies of oriS may be rationalized by its location in a repeated c region of the genome. However, neither copy of oriS is essential because deletion of one or both copies of oriS has no effect on viral DNA replication in cultured cells (1Roizman B. Sears A.E. Fields B.N. Knipe D.M. Howley P.M. Fields Virology. Lippincott-Raven, Philadelphia, PA1996: 2231-2295Google Scholar). The development of a transient DNA replication assay in which origin-containing plasmids are replicated by transfected HSV-1 sequences that supply trans-acting factors led to major advances in the identification of the essential HSV-1 DNA replication genes (4Challberg M.D. Proc. Natl. Acad. Sci. U. S. A. 1986; 83: 9094-9098Crossref PubMed Scopus (140) Google Scholar). This analysis permitted identification of seven HSV-1 genes all located within the UL segment of the genome that are necessary and sufficient for origin-specific DNA replication:UL5, UL8, UL9, UL29, UL30, UL42, and UL52 (Fig.1) (5Wu C.A. Nelson N.J. McGeoch D.J. Challberg M.D. J. Virol. 1988; 62: 435-443Crossref PubMed Google Scholar, 6McGeoch D.J. Dalrymple M.A. Dolan A. McNab D. Perry L.J. Taylor P. Challberg M.D. J. Virol. 1988; 62: 444-453Crossref PubMed Google Scholar). These assignments were subsequently confirmed by demonstrating that mutations in these genes abrogate viral replication (7Zhu L.A. Weller S.K. J. Virol. 1992; 66: 458-468Crossref PubMed Google Scholar, 8Johnson P.A. Best M.G. Friedmann T. Parris D.S. J. Virol. 1991; 65: 700-710Crossref PubMed Google Scholar). Although the function of the UL29 (single-strand DNA-binding protein) and UL30 (DNA polymerase) gene products had already been identified, the remaining five genes encoded proteins of unknown function. These genes were subsequently correlated with proteins identified by biochemical analyses. The functions of these gene products are summarized in Table I, which also depicts the conservation of DNA replication functions in a variety of organisms/systems.Table IAnalogous DNA replication functions in bacteriophages, bacteria, animal viruses and eukaryotesE. coli/phage λPhage T4Phage T7HSV-1S. cerevisiae bORC, origin recognition complex; MCM, maintenance of minichromosome; PCNA, proliferating cell nuclear antigen; RF, replication factor; FEN, flap endonuclease; RP, replication protein.SV40/Homo sapiensOrigin-binding proteinDnaA/O proteinNoneNoneUL9 proteinORCT antigen/?Helicase-primase loading proteinDnaC/P proteingp59NoneUL8 proteinCdc6 protein?T antigen/?Replicative helicaseDnaBgp41gp4UL5/52 proteinsMCM proteins?T antigen/?PrimaseDnaGgp61gp5UL5/52 proteinsDNA pol α-primaseDNA pol α-primaseDNA polymeraseDNA pol IIIapol, polymerase.gp43gp5UL30/42 proteinsDNA pol δ/ɛ?DNA pol δ/DNA pol δ/ɛ?Proofreading exonucleaseɛ subunitgp43gp5UL30 proteinDNA pol δ/ɛ?DNA pol δ/DNA pol δ/ɛ?DNA polymerase clampβ subunitgp45E. coli thioredoxinUL42 proteinPCNAPCNADNA polymerase clamp loaderγ complexgp44/62NoneNoneRF-CRF-CSingle-strand DNA-binding proteinSSBgp32gp2.5ICP8RP-ARP-ARNase HRNase Hgp33.2gp6UL30 proteinRNase H1RNase H15′ → 3′-ExonucleaseDNA pol Igp33.2gp6UL12 protein?FEN-1FEN-1a pol, polymerase.b ORC, origin recognition complex; MCM, maintenance of minichromosome; PCNA, proliferating cell nuclear antigen; RF, replication factor; FEN, flap endonuclease; RP, replication protein. Open table in a new tab A search for proteins that bind to an HSV-1 origin led to the identification of an HSV-1-induced factor that could recognize sequences within oriS (9Elias P. O'Donnell M.E. Mocarski E.S. Lehman I.R. Proc. Natl. Acad. Sci. U. S. A. 1986; 83: 6322-6326Crossref PubMed Scopus (90) Google Scholar). Further purification of this sequence-specific DNA binding activity led to the identification of an 83-kDa protein that bound to two inverted repeats that flank the A + T region, within oriS, designated Boxes I and II (Fig. 2) (10Elias P. Lehman I.R. Proc. Natl. Acad. Sci. U. S. A. 1988; 85: 2959-2963Crossref PubMed Scopus (91) Google Scholar). In oriL the two Box I sites are flanked by homologous sequences designated Box III, which differ from Box I by only 1 residue but act as low affinity recognition sites for the UL9 protein. In oriS there is only one copy of Box III, 5′ to Box I. Subsequently, it was demonstrated that the origin-binding protein is the product of the UL9 gene (11Olivo P.D. Nelson N.J. Challberg M.D. Proc. Natl. Acad. Sci. U. S. A. 1988; 85: 5414-5418Crossref PubMed Scopus (121) Google Scholar). The UL9 gene encodes an 851-amino acid polypeptide (UL9 protein) with a calculated mass of 94,246 Da (12McGeoch D.J. Dalrymple M.A. Davison A.J. Dolan A. Frame M.C. McNab D. Perry L.J. Scott J.E. Taylor P. J. Gen. Virol. 1988; 69: 1531-1574Crossref PubMed Scopus (1231) Google Scholar). Amino acid sequence analysis of the UL9 protein led to the identification of conserved ATP binding and DNA helicase motifs (13Walker J.E. Saraste M. Runswick M.J. Gay N.J. EMBO J. 1982; 1: 945-951Crossref PubMed Scopus (4257) Google Scholar, 14Gorbalenya A.E. Koonin E.V. Donchenko A.P. Blinov V.M. Nucleic Acids Res. 1989; 17: 4713-4730Crossref PubMed Scopus (830) Google Scholar) that have been shown to be essential for viral replication (15Martinez R. Shao L. Weller S.K. J. Virol. 1992; 66: 6735-6746Crossref PubMed Google Scholar, 16Stow N.D. Hammarsten O. Arbuckle M.I. Elias P. Virology. 1993; 196: 413-418Crossref PubMed Scopus (60) Google Scholar). The sequence-specific DNA binding activity of the UL9 protein resides in the C-terminal 317 amino acids (16Stow N.D. Hammarsten O. Arbuckle M.I. Elias P. Virology. 1993; 196: 413-418Crossref PubMed Scopus (60) Google Scholar). Expression of the 37-kDa C-terminal DNA-binding domain has a dominant negative effect on viral replication, presumably because of its ability to occupy the origin nonproductively (16Stow N.D. Hammarsten O. Arbuckle M.I. Elias P. Virology. 1993; 196: 413-418Crossref PubMed Scopus (60) Google Scholar, 17Perry H.C. Hazuda D.J. McClements W.L. Virology. 1993; 193: 73-79Crossref PubMed Scopus (27) Google Scholar). Although the UL9 protein can bind to its recognition sequence as a homodimer, only one of the two monomers contacts the DNA (18Lee S.S-K. Lehman I.R. J . Biol . Chem. 1999; 274: 18613-18617Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar). The dimerization of UL9 protein is mediated through the N-terminal part of the protein, presumably through a leucine zipper motif encompassing residues 150–171 (19Elias P. Gustafsson C.M. Hammarsten O. Stow N.D. J. Biol. Chem. 1992; 267: 17424-17429Abstract Full Text PDF PubMed Google Scholar, 20Deb S. Deb S.P. J. Virol. 1991; 65: 2829-2838Crossref PubMed Google Scholar). The binding of UL9 protein to oriS appears to be enhanced by nucleoside triphosphates (21Gustafsson C.M. Falkenberg M. Simonsson S. Valadi H. Elias P. J. Biol. Chem. 1995; 270: 19028-19034Abstract Full Text Full Text PDF PubMed Scopus (23) Google Scholar). In addition to its sequence-specific DNA binding activity, the UL9 protein possesses DNA-stimulated nucleoside triphosphatase and nonspecific 3′ → 5′-DNA helicase activities (22Bruckner R.C. Crute J.J. Dodson M.S. Lehman I.R. J. Biol. Chem. 1991; 266: 2669-2674Abstract Full Text PDF PubMed Google Scholar, 23Fierer D.S. Challberg M.D. J. Virol. 1992; 66: 3986-3995Crossref PubMed Google Scholar, 24Dodson M.S. Lehman I.R. J. Biol. Chem. 1993; 268: 1213-1219Abstract Full Text PDF PubMed Google Scholar, 25Boehmer P.E. Dodson M.S. Lehman I.R. J. Biol. Chem. 1993; 268: 1220-1225Abstract Full Text PDF PubMed Google Scholar). ICP8, the HSV-1 single-strand DNA-binding protein, interacts with the extreme C terminus of the UL9 protein, greatly stimulating its DNA-dependent ATPase and DNA helicase activities (25Boehmer P.E. Dodson M.S. Lehman I.R. J. Biol. Chem. 1993; 268: 1220-1225Abstract Full Text PDF PubMed Google Scholar). In the absence of ICP8 the UL9 protein is non-processive. ICP8 appears to stimulate the UL9 protein by preventing its dissociation from the DNA (25Boehmer P.E. Dodson M.S. Lehman I.R. J. Biol. Chem. 1993; 268: 1220-1225Abstract Full Text PDF PubMed Google Scholar, 26Boehmer P.E. Lehman I.R. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: 8444-8448Crossref PubMed Scopus (90) Google Scholar). The UL9 protein, together with ICP8, can unwind specifically Box I of oriS if an appropriately oriented 3′ single-stranded tail of at least 18 nucleotides (the binding site size for ICP8; see below) is attached to Box I (27Lee S.S-K. Lehman I.R. Proc. Natl. Acad. Sci. U. S. A. 1998; 94: 2838-2842Crossref Scopus (51) Google Scholar). This finding suggests that a complex consisting of the UL9 protein and ICP8 bound to appropriately oriented single-stranded DNA constitutes the specific helicase that can separate the two strands, permitting entry of the DNA replication machinery. The single-stranded DNA-binding site for ICP8 in oriS may be provided by the A + T sequence that links Boxes I and II. Because of its relatively weak hydrogen bonding, this sequence may be easily unwound, either by the UL9 protein itself or as a consequence of the initiation of transcription at the promoters that flank the origin. This mode of unwinding of an HSV-1 origin by the UL9-protein-ICP8-single-stranded DNA complex differs from that seen with the SV40 T antigen, in which the T antigen itself is the origin-specific helicase and the SSB plays a purely passive role binding the single strands generated by helicase action and thereby preventing their reannealing (28Borowiec J.A. DePamphilis M.L. DNA Replication in Eukaryotic Cells. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY1996Google Scholar). ICP8 is the product of the UL29 gene (29Quinn J.P. McGeoch D.J. Nucleic Acids Res. 1985; 13: 8143-8163Crossref PubMed Scopus (123) Google Scholar) and consists of 1196 amino acids with a calculated molecular mass of 128,342 Da. ICP8 binds single-stranded DNA rapidly and cooperatively and with at least 5-fold greater affinity than double-stranded DNA (30Ruyechan W.T. J. Virol. 1983; 46: 661-666Crossref PubMed Google Scholar, 31Lee C.K. Knipe D.M. J. Virol. 1985; 54: 731-738Crossref PubMed Google Scholar). Examination of ICP8 binding to single-stranded DNA, by electron microscopy and negative staining, showed regular protein-DNA filaments in which the DNA is held in an extended configuration (32Ruyechan W.T. Weir A.C. J. Virol. 1984; 52: 727-733Crossref PubMed Google Scholar, P.E. Lehman I.R. J. Biol. PubMed Scopus Google Scholar). of the DNA-binding site size for ICP8 in the of one ICP8 to nucleotides P.E. Lehman I.R. J. Virol. 1993; PubMed Google Scholar, Lehman I.R. J. Virol. 1993; PubMed Google Scholar, Lehman I.R. J. Biol. Chem. Full Text PDF PubMed Google that are in with a site size of nucleotides by electron microscopy P.E. Lehman I.R. J. Biol. PubMed Scopus Google Scholar). The HSV-1-encoded primosome consists of three with molecular of and the products of the UL8, genes, D.J. Dalrymple M.A. Dolan A. McNab D. Perry L.J. Taylor P. Challberg M.D. J. Virol. 1988; 62: 444-453Crossref PubMed Google Scholar). The consists of a of the UL8, and UL52 gene with a molecular mass of J.J. T. L.A. Weller S.K. P.D. Challberg M.D. Mocarski E.S. Lehman I.R. Proc. Natl. Acad. Sci. U. S. A. 1989; PubMed Scopus Google Scholar, M.S. Crute J.J. R.C. Lehman I.R. J. Biol. Chem. 1989; Full Text PDF PubMed Google Scholar). A that consists of the and UL52 DNA-dependent and activities and constitutes the Stow N.D. Nucleic Acids Res. PubMed Scopus Google Scholar, M.S. Lehman I.R. Proc. Natl. Acad. Sci. U. S. A. 1991; PubMed Scopus Google Scholar). In the protein detectable or DNA binding activities M.S. Lehman I.R. Proc. Natl. Acad. Sci. U. S. A. 1991; PubMed Scopus Google Scholar, M.E. Stow N.D. J. Gen. Virol. 1993; PubMed Scopus Google Scholar). the appropriate of and the helicase activity of the can unwind a consistent with the of for the of in during replication of virus, herpesvirus M. Elias P. Lehman I.R. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). of the UL52 protein contain a binding motif that is conserved in DNA and Challberg M.D. J. Virol. PubMed Google S. Koonin E.V. Crute J.J. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar). of this motif the activity of the in and origin-specific DNA replication in vivo, that it the The products of action are that are in J.J. Lehman I.R. J. Biol. Chem. 1991; 266: Full Text PDF PubMed Google Scholar, J. Challberg M.D. J. Virol. 1992; 66: PubMed Google Scholar). single-stranded DNA as the sequence The sequence was to the synthesis of a at the C residue D.J. M. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar). The protein synthesis by the D.J. P.A. M. J. Biol. Chem. Full Text PDF PubMed Google Scholar, D.J. M. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar, M. Elias P. Lehman I.R. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). protein has no effect on of the it the of synthesis D.J. P.A. M. J. Biol. Chem. Full Text PDF PubMed Google Scholar). The protein is also required for DNA helicase and DNA-dependent ATPase activities of the in the of DNA M. Elias P. Lehman I.R. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, P.E. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus (51) Google Scholar). It the loading factors seen in other Table The DNA-binding protein for ICP8, a specific between ICP8 and the protein. in fact, an between ICP8 and the but not with the or the protein M. Elias P. Lehman I.R. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). The HSV-1 DNA polymerase has been both as a DNA polymerase and as a for It is a protein that is encoded by the UL30 gene (29Quinn J.P. McGeoch D.J. Nucleic Acids Res. 1985; 13: 8143-8163Crossref PubMed Scopus (123) Google Scholar, D.J. PubMed Scopus Google Scholar, H.C. M.J. Weller S.K. D.M. Proc. Natl. Acad. Sci. U. S. A. 1985; PubMed Scopus Google Scholar, D.M. 1986; PubMed Scopus (23) Google Scholar). The UL30 protein sequence to other viral and cellular DNA human DNA polymerase cerevisiae DNA polymerase coli DNA polymerase I, and the bacteriophage DNA polymerase P. D.M. J. Biol. Chem. Full Text PDF PubMed Google Scholar, L. A. M.A. M. 1991; PubMed Scopus Google Scholar). The HSV-1 DNA polymerase from cells exists as a in which the UL30 protein is associated with a protein J. Virol. 1985; PubMed Google Scholar, M.L. M. Parris D.S. J. Virol. 1988; 62: PubMed Google Scholar, J.J. Lehman I.R. J. Biol. Chem. 1989; Full Text PDF PubMed Google Scholar). The protein is the product of gene which encodes a that possesses DNA binding activity D.J. Dalrymple M.A. Dolan A. McNab D. Perry L.J. Taylor P. Challberg M.D. J. Virol. 1988; 62: 444-453Crossref PubMed Google D.S. A. L. A. Frame M.C. M. McGeoch D.J. J. Virol. 1988; 62: PubMed Google Scholar). The between the UL30 and proteins with an of 1 M. D.J. M.G. J. Gen. Virol. 1993; PubMed Scopus Google Scholar) and has been shown to be essential for viral replication P. D.M. J. Virol. 1993; PubMed Google Scholar). The HSV-1 DNA polymerase possesses 3′ → activity that is to the UL30 J. Biochem. PubMed Scopus Google Scholar, M.E. Elias P. Lehman I.R. J. Biol. Chem. Full Text PDF PubMed Google Scholar). The is that are for deoxynucleotide and can act on a variety of DNA DNA, DNA and single-stranded M.E. Elias P. Lehman I.R. J. Biol. Chem. Full Text PDF PubMed Google Scholar). In the absence of the 3′ → is as at as In the of all four there is no detectable 3′ → on presumably because of In are M.E. Elias P. Lehman I.R. J. Biol. Chem. Full Text PDF PubMed Google Scholar). the 3′ → as a activity to of DNA replication. In addition to its 3′ → the HSV-1 DNA polymerase has a activity that presumably to RNA during the of J.J. Lehman I.R. J. Biol. Chem. 1989; Full Text PDF PubMed Google Scholar). The protein acts to the of the UL30 DNA polymerase Lehman I.R. J. Biol. Chem. Full Text PDF PubMed Google Scholar, M.L. Parris D.S. J. Virol. 1989; PubMed Google Scholar, J. D.M. Challberg M.D. J. Virol. PubMed Google Scholar). It is a of the DNA polymerase which include the β of coli DNA polymerase the proliferating cell nuclear antigen, and bacteriophage gene 45 protein (28Borowiec J.A. DePamphilis M.L. DNA Replication in Eukaryotic Cells. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY1996Google Scholar, R. O'Donnell M.E. J. 1992; 69: Full Text PDF PubMed Scopus Google Scholar) Table These proteins a that the DNA duplex and with their DNA polymerase to dissociation of the from the thereby of deoxynucleotide However, these DNA polymerase DNA binding activity, and their on the DNA is mediated by set of the clamp In the HSV-1 DNA polymerase is to the DNA by the DNA binding activity of the protein This is by the finding that of DNA polymerase activity requires the DNA binding activity of the protein M.L. Parris D.S. J. Virol. 1989; PubMed Google Scholar, J. D.M. Challberg M.D. J. Virol. PubMed Google Scholar). and have been for their ability to viral replication in and to the HSV-1 DNA polymerase in This has led to the development of and which are of H.C. M.J. Weller S.K. D.M. Proc. Natl. Acad. Sci. U. S. A. 1985; PubMed Scopus Google Scholar). In addition to ICP8, the DNA the UL9 protein, and the DNA helicase-primase, all of which are essential for HSV-1 DNA replication, the HSV-1 genome encodes a set of enzymes whose function is not required for its replication in cultured serve some function in the viral life These include an that 5′ → activity protein) and may in the of DNA synthesis, a DNA a a and a P.E. Lehman I.R. Annu. Rev. Biochem. 1997; 66: 347-384Crossref PubMed Scopus (268) Google Scholar). As of HSV-1 DNA replication in have demonstrated that the linear 153-kilobase genome shortly after of cells and a rolling circle mode of DNA replication branched DNA, which is and as The existence of specific origins of replication oriS or oriL as as a protein (the UL9 protein) with helicase activity that binds the origins with affinity suggests that a theta mode of DNA replication the rolling circle phase (Fig. A mode of DNA replication of this has been observed for bacteriophage λ (3Stahl F.W. Stahl M.M. Hershey A.D. The Bacteriophage Lambda. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY1971: 195-210Google Scholar). as rolling circle replication of the HSV-1 genome as as of plasmids which an HSV-1 origin has been has been observed in vivo, there is as yet no for a theta mode of replication. have been to origin or DNA replication in has been In to the to the theta of HSV-1 DNA replication, rolling circle replication by of cells has been The first of rolling circle replication of an replication consisting of single-stranded DNA to which a with an 5′ single-stranded tail had been circle replication was observed both with of cells and with a the HSV-1 DNA polymerase and the and UL52 of the DNA ICP8 the but was not essential B. J. Virol. PubMed Google Scholar). In a a molecular mass complex was by and from of cells that had been infected with for the seven HSV-1 genes that are required for its replication. This which of the HSV-1 DNA polymerase, ICP8, and DNA helicase-primase, could the rolling circle replication of to DNA up to four times as by and electron the UL9 protein an HSV-1 origin was and in fact, the of oriS within the DNA replication in the but not the of the UL9 protein R. Lehman I.R. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). of human cells can also the rolling circle replication of in a that that observed with the molecular complex from the cells R. Lehman I.R. J. Virol. PubMed Google Scholar). suggests that a similar complex is in the Although the of in these has not been it to the in However, the of the is low of the for both the complex from the cells and the of The of the DNA that as the for rolling circle replication is not and the of the replicated may the low of the appropriate that is generated by either the complex or the a event to that which appears to be involved in the from theta to rolling circle replication in bacteriophage λ may be required (3Stahl F.W. Stahl M.M. Hershey A.D. The Bacteriophage Lambda. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY1971: 195-210Google Scholar). In HSV-1 is a large double-stranded DNA virus whose genome contains origins of replication. HSV-1 encodes a of proteins with the of a DNA and to initiate and DNA replication. The is that following circularization of the linear HSV-1 replication by theta by rolling circle DNA replication. A DNA polymerase, DNA polymerase may function during phase Lehman I.R. Proc. Natl. Acad. Sci. U. S. A. 1995; PubMed Scopus Google Scholar) (Fig. the functions of the HSV-1 DNA replication proteins found in other conservation in the of DNA replication.