of each duplication joint was determined. The genome of ... HSV-1 strain Patton were prepared as follows. .... data that substantiated this are described below.
JOURNAL
OF
VIROLOGY, Feb. 1985, p. 607-615
Vol. 53, No. 2
0022-538X/85/020607-09$02.00/0 Copyright C 1985, American Society for Microbiology
Isolation of Novel Herpes Simplex Virus Type 1 Derivatives with Tandem Duplications of DNA Sequences Encoding Immediate-Early mRNA-5 and an Origin of Replication KENICHI UMENEt* AND LYNN W. ENQUISTt Laboratory of Molecular Virology, National Cancer Institute, Bethesda, Maryland 20205 Received 25 June 1984/Accepted 24 October 1984
Two naturally occurring variations of herpes simplex virus type 1 (Patton strain) with novel tandem DNA duplications in the S component were isolated, and the DNA was characterized. These variants were identified among a number of plaque isolates by the appearance of new restriction enzyme fragments that hybridized with radiolabeled DNA from the BamHI Z fragment (map coordinates 0.936 to 0.949) located in the unique S region. One isolate, SP26-3, carried a 3.1-kilobase-pair duplication defined by recombination between a site in the BamHI Z fragment and a site near the origin of replication in the inverted repeat sequence of the S component carried by the EcoRI H fragment. The other isolate, SP22-4, carried a 3.5-kilobase-pair duplication defined by a recombination event between a tandem repeat array in the BamHI Z fragment and a site near the amino terminus of the Vmwl75 gene in the S-region inverted repeat sequence contained in the EcoRI K fragment. Both duplicated segments contained the entire immediate early mRNA-5 coding region as well as the origin of replication located in the inverted repeat sequence of the S component. The DNA sequence of each duplication joint was determined. sequence
The genome of herpes simplex virus (HSV) is remarkable for its unusual structure. The DNA itself is a linear, doublestranded molecule of ca. 160 kilobase pairs (kb), consisting of two covalently linked components, L and S, that constitute ca. 82 and 18% of the genome, respectively (Fig. 1A). A short sequence, a, is repeated directly at the termini of the HSV genome and is also present in the inverse orientation at the L-S junction (15). The a sequences are implicated in the isomerization of the genome, whereby the L and S segments of the HSV genome invert, yielding four structural isomers (1, 9-11). A different kind of structural rearrangement of the HSV genome occurs after serial passage of HSV at high multiplicities of infection. The virus preparations so obtained contain defective interfering particles. The DNA isolated from these particles consists of multiple head-to-tail reiterations of specific HSV sequences (3, 4, 6). The class I defective DNA of HSV type 1 (HSV-1) strain Patton can be formed by a hypothetical recombinational event between the terminal S-region a sequence and a site within the BamHI Z fragment (the B5B6 fragment of reference 2) (Fig. 1). In this report, we present another structural alteration of HSV-1 DNA that occurred in our laboratory stocks. We describe the isolation and analysis of two HSV-1 (Patton) derivatives with unique duplications in the S component.
essential medium with 2% fetal bovine serum. The multiplicity of infection was 0.01 PFU per cell. Single-plaque isolates from HSV-1 strain Patton used in this work are summarized in Table 1. HSV-1 DNA was prepared from viral particles obtained after glycerol gradient centrifugation as described by Denniston et al. (2). Plasmids and phage. Bacteriological methods were as described by Umene and Enquist (17). The Escherichia coli host for the experiments was LE392. Hybrid plasmids used in this work are given in Table 1, and they were grown and purified as described by Denniston et al. (2). A hybrid lambda phage, Dec24, carries the EcoRI H fragment of HSV-1 strain Patton, and its DNA was extracted as described by Umene and Enquist (17). Gel electrophoresis and Southern hybridization. Restriction endonucleases were purchased from New England Biolabs, Inc., Beverly, Mass., or from Bethesda Research Laboratories, Inc., Rockville, Md., and digestion conditions were those recommended by the manufacturers. DNA markers, agarose and acrylamide gel procedures, Southern transfer, and hybridization conditions have been presented by Denniston et al. (2). DNA sequencing. The nucleotide sequences were determined as described by Maxam and Gilbert (8).
MATERIALS AND METHODS
RESULTS
Cells and viruses. Vero cells were grown in minimal essential medium supplemented with 5% calf serum. Stocks of HSV-1 strain Patton were prepared as follows. Virus from single plaques was used to infect Vero cells in minimal *
Isolation of HSV-1 strain Patton derivatives carrying duplications of sequences involving the BamHI Z fragment. We have previously reported that the BamHI Z fragment (B5B6 fragment) of HSV-1 strain Patton varies in size among independent single-virus plaque isolates (17). This heterogeneity was due to a difference in tandem repeat number of a 15-base-pair (bp) sequence (Fig. 1B and C) (17a). We examined the fragment polymorphism of the BamHI Z fragment in more detail, and DNA from a number of single-plaque isolates of HSV-1 strain Patton was digested with BamHI
Corresponding author.
t Present address: Department of Virology, Faculty of Medicine,
Kyushu University, Fukuoka 812, Japan. t Present address: E. I. du Pont de Nemours & Co., Inc., Central Research and Development, Experimental Station, Wilmington, DE 19898. 607
608
UMENE AND ENQUIST
J. VIROL. .#
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FIG. 1. Maps of HSV-1 DNA. (A) Structure of the HSV-1 genome. HSV-1 DNA consists of two covalently linked components designated L and S. Each component consists of unique sequences (UL and Us) bracketed by inverted repeat sequences (TRL, IRL, IRS, and TRs). The short a sequence is noted. The EcoRI H and K fragments are designated H and K, respectively. (B) Map of the S region of HSV-1. BamHl sites (Bi to B8), EcoRI sites (RI), and a Sall site are indicated. The BamHI Z fragment (B5B6) is indicated by a hatched box. Sall-B5 region cloned into pBR322 (pBS127-2) is indicated. (C) Map of the BamHI Z (B5B6) fragment. MboII sites (Ml to M4), HpaII sites (Hp), and a Sall site (S1) are shown. A sequence of tandem 15-bp repeats is indicated by a solid box (17a). The 3' end of IEmRNA-5 is indicated (19). Similarly, the 3' ends of three early mRNAs transcribed from the opposite strand are indicated (17a). (D) Map of the BamHI X (B3B4) fragment. The EcoRI site (RI) and five SmaI sites (S) are indicated. The 90-bp origin of replication (16) is indicated by a solid box. The 5' end of IEmRNA-5 is indicated (19).
and electrophoresed on an agarose gel. After transfer to a nitrocellulose filter, the DNA fragments were hybridized with a 32P-labeled BamHI Z probe (the SalI-BamHI subfragment cloned in pBS127-2) (Fig. 1B, Table 1). Unexpectedly, in some viral DNA preparations, we observed not only the BamHI Z fragment on the autoradiography but also three other fragments (Fig. 2). One isolate, SP26, had in addition to BamHI Z two extra BamHI fragments of 2.9 and 5.9 kb that hybridized with pBS127-2 (Fig. 2, lane 1). Another isolate, SP22, had a single extra BamHI fragment of 1.4 kb (Fig. 2, lane 6). These anomolous BamHI fragments were maintained during passage of each virus stock. For example, four single plaques of SP26 and six single plaques of SP22 were isolated, and the DNA of the secondary single-plaque isolates was propagated and analyzed. All four SP26 secondary singleplaque isolates retained the two extra BamHI fragments of 2.9 and 5.9 kb. One isolate, SP26-3, was analyzed further. The anomolous BamHI fragment from SP22 was less stable. Out of six secondary single-plaque isolates, only one (SP22-4) retained the 1.4-kb BamHI fragment. Composition and origin of new BamHI fragments. The new BamHI fragments of SP26-3 and SP22-4 were first cloned in pBR322. The hybrid plasmids carrying the 5.9-, 2.9-, and 1.4-kb novel BamHI fragments were named pUK171, pUK172, and pUK174, respectively (Table 1).
The origin of these novel BamHI fragments was determined by labeling each hybrid plasmid with 32P and then using these probes in Southern blot hybridization experiments with viral and cloned HSV-1 DNA fragments. Initially, we assumed that the new BamHI fragments were likely to be derived from the S region because they hybridized to a BamHI Z fragment probe. This assumption was subsequently proven correct, and some of the hybridization data that substantiated this are described below. When the BamHI Z probe (pBS127-2) was labeled and hybridized to EcoRI-digested viral DNA isolated from SP26-3 and SP22-4, we expected the EcoRI H fragment (BamHI-Z is contained within EcoRI-H) to be the only EcoRI fragment visible. Instead, the probe hybridized to a distinctive set of fragments (Fig. 3). For SP26-3 DNA, the majority of the fragments were longer than the EcoRI H fragment of our standard HSV-1 isolate (SP23). In addition, the EcoRI digests of SP22-4, but not SP26-3, revealed a new 3.5-kb fragment visible after ethidium bromide staining that hybridized with the BamHI Z probe. The simplest explanation for the appearance of the new BamHI and EcoRI fragments is that they result from tandem duplications of BamHI Z DNA sequences (Fig. 4). These conclusions were substantiated by detailed mapping of the DNA sequences contained by plasmids pUK171, pUK172, and pUK174, both by direct restriction enzyme mapping and
VOL. 53, 1985
HSV-1 S-REGION DUPLICATIONS
by hybridization experiments with bacteriophage lambda hybrids carrying HSV-1 EcoRI-H (Dec24). Structures of HSV-1 genomes with novel duplications. When DNA from stocks of SP22-4 and SP26-3 was analyzed, it became clear that the duplications as drawn in Fig. 4 existed in several permutations. For example, stocks of SP22-4 predominantly contained genomes with the same 3.5-kb duplication on both sides of the S region (Fig. SA). This was most easily seen by cleaving with enzymes that have unique sites in Us and in the duplicated sequence (Fig. 5B and 6). For example, XhoI cleavage of SP22-4 DNA generated novel fragments of 4.0 and 3.4 kb that hybridized with a cloned EcoRI H probe (Fig. 5B and 6). The 3.4-kb fragment derived from genomes with the duplication on the right side of S, and the 4.0-kb fragment comes from genomes with the duplication on the left. Corroborating results were obtained with other enzymes (Fig. 5B and 6). It was possible to deduce that most of the genomes contained only duplications and not triplications or higher reiterations by cleaving SP22-4 DNA with enzymes that do not cut in the duplicated sequence. For example, when SP22-4 was cleaved with BglII and hybridized with an EcoRI H probe, two novel fragments of 20.5 and 13 kb were observed; HindIII cleavage gave two fragments of 11 and 17.5 kb (Fig. SB and 6). Fragments of these sizes are predicted only from duplicated sequences. Our analysis of SP26-3 stocks indicates that the duplication exists in at least two permutations (Fig. 7A). One population of genomes has the structure as diagrammed in Fig, 4B. It contained one copy of the duplication defined by the 2.9-kb BamHI fragment (pUK172) on the right side of S plus one copy of the duplication defined by the 5.9-kb BamHI fragment (pUK171) on the left side of S. The other population contained two copies of the duplication defined by the 2.9-kb BamHI fragment on the right side of S plus one copy of the same duplication adjacent to the duplication
l
TABLE 1. Virus, phage, and plasmids Strain
Description
HSV-1 strain Patton SP22 Single-plaque isolate SP23 Single-plaque isolate (used as a standard isolate) SP24 Single-plaque isolate SP25 Single-plaque isolate SP26 Single-plaque isolate SP27 Single-plaque isolate SP22-4 Single-plaque isolate from SP22 SP26-3 Single-plaque isolate from SP26
Phage Dec24 Plasmids pBS127-2
pUK171 pUK172
pUK174
Reference
Graham et al. (4) This report This report
This This This This This This
report report report report report report
Lambda hybrid phage carrying HSV-1 EcoRI H fragment
Umene and Enquist (17)
pBR322 derivative carrying SallBamHI (B5) fragment on HSV-1 EcoRI H fragment pBR322 derivative carrying a 5.9-kb new BamHI fragment of SP26-3 pBR322 derivative carrying a 2.9-kb new BamHI fragment of SP26-3 pBR322 derivative carrying a 1.4-kb new BamHI fragment of SP22-4
Denniston et al. (2)
This report
2 3 4 5 6
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FIG. 2. Southern hybridization profiles of BamHI digests of single-plaque isolates of HSV-1 strain Patton, using 32P-labeled pBS127-2 as a probe. Lanes: 1, SP26; 2, SP27; 3, SP25; 4, SP24; 5, SP23; 6, SP22 (see Table 1). The sizes of the fragments are indicated in kb. The BamHI Z (B6B5) fragment was detected in all isolates as a fragment with heterogeneous length (1.8 to 2.0 kb) (17a). Trhe novel BamHI fragments in SP26 (lane 1) and SP22 (lane 6) are indicated.
defined by the 5.9-kb BamHI fragment on the left side of S (Fig. 7A). This was deduced by a digestion of SP26-3 DNA with the enzymes described in Fig. 7B and 8B. For example, in a Sacl plus EcoRI digestion, four fragments of 10.4, 7.7, 7.3, and 4.6 kb hybridizing to cloned EcoRI-H were observed (Fig. 8B, lane 3). These fragments can only be derived from the structures diagrammed in Fig. 7A, as the predicted fragments from the structure are shown in Fig. 7B. Four extra EcoRI H fragments were detected in the EcoRI digests of SP26-3 after hybridization with cloned EcoRI-H (Dec24) (Fig. 8A). The 18.5-kb EcoRI fragment can be derived from the genome with only one duplication on either side of S (Fig. 7). The 25-kb EcoRI fragment can be derived from the genome with one duplication on one side of S plus
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FIG. 3. Analysis of EcoRI fragments that hybridize to a BamHI Z probe. EcoRI-cut viral DNAs after electrophoresis on a 1% agarose gel were hybridized with 32P-labeled pBS127-2 DNA on a nitrocellulose filter. Lanes: 1, wild-type viral DNA (SP23); 2, SP26-3; 3, SP22-4; M, HindIll fragments of lambda phage DNA. The sizes of the fragments are indicated in kb. The EcoRI H
fragment is indicated.
610
UMENE AND ENQUIST
J. VIROL. duplication novel EcoRI fragment
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pUKl 72 FIG. 4. Structure of the duplications carried by SP22-4 and SP26-3. (A) The SP22-4 duplication. BamHI sites (Bi to.B8) and EcoRI sites (RI) are indicated. The solid boxes indicate inverted repeat sequences of S component. The boxes with vertical lines indicate the 15-bp tandem repeat array found in BamHI-Z (Fig. 1C) (17a). The duplication is indicated by a horizontal arrow above the line. The novel EcoRI fragment is indicated. The novel BamHl fragment cloned in pUK174 is shown below the line. The novel joint is indicated by a vertical arrow. (B) The SP26-3 duplication. The symbols are the same as described above. The two novel BamHI fragments cloned in pUK171 and pUK172 are indicated below the line.
pUKl 71
two duplications on the other side of S (Fig. 7). The other EcoRI H fragments can be explained as drawn in Fig. 7. From SP26-3, two novel BamHI fragments were cloned in pUK171 and pUK172. The diagram of the SP26-3 duplication in Fig. 7A adequately describes the two BamHI fragments. The two novel BamHI fragments may derive from the same duplication event (Fig. 9). The short duplicated segment of inverted repeat sequences of S component provides homology for intramolecular inversion on the molecule of line 1 of Fig. 9 (wavy line) as well as unequal intermolecular recombination between the molecules of line 1 and line 2 of Fig. 9, either one of which will create the second novel BamHI fragment. The initial duplication could have created either the 2.9- or 5.9-kb BamHI fragment, and subsequent recombination would yield the other. The initial recombinational event might have been the essential step for the generation of HSV-1 genome with the duplications. Once a duplication was made, it could propagate (Fig. 9). Sequence analysis of the novel junctions in the new BamHI fragments. The nucleotide sequence of each junction in the new BamHI fragments was determined and compared with corresponding known sequences in the HSV-1 genome (Fig. 10). The nucleotide sequence across the novel joint of pUK171 and pUK172 was identical (Fig. 10). With the numbering system of Watson and Vande Woude (19), the EcoRI site in inverted repeat sequence of S component is used as the reference point. The noncoding strand with respect to the immediate early mRNA-5 (IEmRNA-5) gene is presented. The novel joint found in the BamHI fragment cloned in pUK171 and pUK172 is defined by a fusion of
residue 79 (G) to residue 2891 (G) located in the MboII2-MboII-3 fragment of BamHI-Z (Fig. 1C). One segment of the novel joint of pUK174 was defined similarly, using the EcoRI site in inverted repeat sequence of S component as the reference point. However, the other segment was derived from DNA encoding Vmwl75 (13). We have used the numbering system of Murchie and McGeoch (13) to define the site in Vmw175. The novel joint carried by pUK174 was formed by fusing 68 codons of the amino terminus of Vmwl75 (residue 1346, G) to the residue 2750 plus 20 of the second 15-bp repeat in the BamHI Z fragment (Fig. 10D, E, and F).
DISCUSSION We describe in this report the isolation and characterization of two HSV-1 plaque isolates that contain DNA with novel duplications in the S region. Duplications of this general type have been described previously (5) among recombinants derived from marker rescue experiments with Vmwl75 temperature-sensitive mutations. Our observations relate to spontaneous duplications and the detailed analysis of the DNA structure. The novel joint of the SP26-3 duplication fuses DNA between the IEmRNA-3 and IEmRNA-5 transcripts with DNA in the BamHI Z fragment (Fig. 4B). The duplication joint is located between two promoters, one 0.5 kb upstream of the 5' transcribed region of the IEmRNA-5 gene and one 0.2 kb upstream of the 5' transcribed region of the IEmRNA3 (Vmwl75) gene (13, 18, 19). This region also encompasses an active replication origin (16). The DNA defining both the
VOL. 53, 1985
HSV-1 S-REGION DUPLICATIONS
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origin of replication and the transcribed region of IEmRNA5 is entirely included in the duplication. The novel joint of SP22-4 fuses DNA encoding the amino terminus of Vmw175 (68 codons; 0.63 kb from the EcoRI site of the EcoRI H fragment) to the 15-bp tandem repeat array located in the BamHI Z fragment (Fig. 4A) (13, 19). The duplicated sequence of SP22-4 contains the total transcribed region of IEmRNA-5 and a truncated transcribed region of IEmRNA-3. In addition, it also contains an apparently complete replication origin, as defined by Stow and McMonagle (16). Given the mechanisms to generate duplications, one must consider the capacity of the HSV DNA-packaging system. How much DNA can the capsid contain? An analysis of recombinants produced by rescue of HSV-1 temperaturesensitive mutants with HSV-2 DNA fragments indicated the possibility of adding more than 8 kb to the S component (5). Our data indicate that even more DNA can be added to the S component. We detected four extra EcoRI H fragments in SP26-3 viral DNA, the largest being 28 kb (Fig. 8A). This indicates that HSV-1 particles can be formed with a genome longer than wild type by at least 12.6 kb (28 to 15.4 kb;
normal EcoRI-H) if other parts of the HSV-1 genome are not deleted. There was no evidence of any larger EcoRI H fragments. These apparently are not packaged or, if packaged, are not maintained as stable particles. Perhaps larger duplications are more readily lost during replication due to homologous recombination events between duplicated segments. In fact, the molar quantity of the 28-kb EcoRI H fragment was reduced, suggesting that the genome containing the 28-kb EcoRI H fragment might not have been stable or the DNA not efficiently packaged. The DNA sequence of the regions involved in the duplications contains several noteworthy segments. One curious observation is a potential DNA gyrase cleavage sequence at the site of the SP26-3 duplication. DNA gyrase has been previously suggested to promote certain recombination events in E. coli and eucaryotic cells (7). The consensus sequence, 5'-Py Pu T G X Py X X Py-3' (Py, pyrimidine; Pu, purine; X, random base), for an E. coli gyrase site was proposed by Morrison and Cozzarelli (12). The site of the SP26-3 duplication in BamHI Z has the sequence 5'TGCGGTCTT-3' (italicized G is the residue 2891/79 in Fig. 10B), which corresponds to the consensus sequence except
HSV-1 S-REGION DUPLICATIONS
VOL. 53, 1985
613
(B)
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0.6FIG. 8. Southern hybridization profiles of restriction c-nzyme digests of SP23 (parent; lane p) and SP26-3 (duplication; lane d), using a 32P-labeled EcoRI H fragment (Dec24) as a probe. The sizes of the fragments are shown in kb. The sizes of the fragments which were detected only in digests of SP26-3 are underlined. (A) Southern hybridization profiles of EcoRI digests after electrophoresis on a 0.5% agarose gel. (B) Southern hybridization profiles of Sall and EcoRI (lane 1), XhoI and EcoRI (lane 2), Sacl and EcoRI (lane 3), PvuI and EcoRI (lane 4), BgIII and EcoRI (lane 5), and KpnI and EcoRI (lane 6) digests after electrophoresis on a 1% agarose gel.
for the third C residue. The significance of the strong homology to an E. coli gyrase cleavage site is not obvious. Analysis of the DNA sequences also implied that short DNA homologies may be involved (7). For example, the sequence 5'-CGG-3' is found at the site of fusion of SP26-3 in
both the EcoRI-SmaI and MboII-2-MboII-3 fragments of the parent virus (Fig. 10A and C). The sequence is not present in the novel fragment of the SP26-3 duplication (Fig. 10B). The viral DNA from stocks containing these duplications contains nonduplicated DNA as well as additional tandem
Int rd molecular pUK 72 1)
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614
UMENE AND ENQUIST
J. VIROL.
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5'--ACGCGCGTGTCGATGCGCCCCGCCCATCCGCGCC---3 i 12891 /79
2875
C. M2-M3
5---AC G CGCGTGTCG ATGCGGT CT T TT AG CGGAGCAG---3 2875 2891 2908
11. pUK174 D. M1-M2
repeat-n
5---T TG(CCACTCCCCACCCAC)(CCACTCCCC ACCCAC)---(
)C C AAA ---3
2750.20 repeat-i
2772
novel4point
5'--T TG(CCACTCCCCACCCAC)tCA GCGTCCTCGCCGGCG TCGGTG C---3 2750
F. AluI-TaqI
repeat-2
repeat-1
2750
E. Ml-TaqI
96
2750-20 1346
1367
5---CGCGGCGAGACGGCGTCCCC GGCGTCCTCGCCGGCGTCGGTGC---3' 1346 1325 1367
FIG. 10. Nucleotide sequence analysis of the novel duplication junctions found in SP22-4 and SP26-3. Lines A, B, and C define the novel junction in SP26-3 (the 2.9- and 5.9-kb BamHI fragments cloned in pUK172 and pUK171, respectively). The numbering system is described in the text and in references 13 and 19. (A) A portion of the EcoRI-SmaI sequence (Fig. 1D) is shown. The 5' C residue of the Smal site of the EcoRI-SmaI segment is at the 225th residue (19). The G residue at number 79 is indicated. (B) Sequence of the novel junction defined by an MboII-2 (M2)-Smal fragment. (C) A portion of the MboII-2 (M2)-MboII-3 (M3) sequence from BamHI-Z (Fig. 1C) is indicated. The DNA sequences presented are those of the noncoding strand of the IEmRNA-5 gene as defined by Watson and Vande Woude (19). Lines D, E, and F define the novel junction in SP22-4 (the 1.4-kb BamHI fragment cloned in pUK174). The numbering system is described in the text and by Umene et al. (17a) for (D) and Murchie and McGeoch (13) for (F). (D) A portion of the 15-bp tandem repeat sequence in BamHI-Z (Fig. 1C) is shown. The A residue at number 2750 plus 20 is indicated. (E) Sequence of the novel junction is indicated. (F) A portion of the sequence of an AluI-TaqI fragment from within the B2B3 BamHI fragment (Fig. 1B). repeats and permutations of the basic duplication. Opportunities abound for recombination and unequal crossing over to generate a variety of novel S-region sequences in stocks of
these viruses. One interesting effect of the duplication in SP26-3 (Fig. 4B) is that each inverted repeat region of S is increased by 3.1 kb (the size of the duplication) (Fig. 7 and 8A). The ramifications of this on L-S inversion and defective particle formation remain to be seen. The biological functions of the duplications observed in SP26-3 and SP22-4 are currently unknown. The selective effects of multiple origins, additional promoters, and IEmRNA-5 segments must be examined. Although not examined in detail, there are no obvious effects of the duplications on virus propagation. It is not clear how frequently these duplications occur in a given virus stock. They were isolated without selection after screening only 30 singleplaque isolates of strain Patton. Similarly, it is not obvious how these duplications relate to those described by Knipe et al. (5). Perhaps this region is recombinogenic due to the presence of replication origins, active promoters, and sets of repetitive DNA sequences. The region is rich with such detail. For example, the IEmRNA-5 region has been analyzed in detail by Rixon and McGeoch (14). They have shown that there are actually three mRNAs specified within this region that encode three partially overlapping genes (Vmwl2, Vmw2l, and Vmw33). These genes specify three mRNAs with distinct 5' termini but a common 3' terminus, the longest of which is IEmRNA-5. They speculate that the Vmw2l protein interacts with DNA. Further study is re-
quired to determine whether these genes are expressed in the duplications. Furthermore, the relationship, if any, of duplication formation and the well-known L-S isomerization reaction and the formation of defective interfering particles remains to be established. ACKNOWLEDGMENT We thank R. Watson for invaluable advice. G. Vande Woude was the lab chief. The major part of this work was funded by intramural research funds from the National Cancer Institute. A minor part was supported by grants from the Ministry of Education, Science and Culture of Japan. The costs for publication of this work were supported by a grant-in-aid from the Fukuoka Cancer Society. LITERATURE CITED
1. Davison, A. J., and N. M. Wilkie. 1981. Nucleotide sequences of the joint between the L and S segments of herpes simplex virus types 1 and 2. J. Gen. Virol. 55:315-331. 2. Denniston, K. J., M. J. Madden, L. W. Enquist, and G. Vande Woude. 1981. Characterization of coliphage lambda hybrids carrying DNA fragments from herpes simplex virus type 1 defective interfering particles. Gene 15:365-378. 3. Frenkel, N. 1981. Defective interfering herpesviruses, p. 91-120. In A. J. Nahmias, W. R. Dowdle, and R. S. Schinazi (ed.), The human herpesviruses-an interdisciplinary prospective. Elsevier/North-Holland Publishing Co., New York. 4. Graham, B. J., Z. Bengali, and G. F. Vande Woude. 1978. Physical map of the origin of defective DNA in herpes simplex virus type 1 DNA. J. Virol. 25:878-887.
VOL. 53, 1985
5. Knipe, D. M., W. T. Ruyechan, B. Roizman, and I. W. Halliburton. 1978. Molecular genetics of herpes simplex virus: demonstration of regions of obligatory and nonobligatory identity within diploid regions of the genome by sequence replacement and insertion. Proc. Natl. Acad. Sci. U.S.A. 75:3896-3900. 6. Locker, H., and N. Frenkel. 1979. Structure and origin of defective genomes contained in serially passaged herpes simplex virus type 1 (Justin). J. Virol. 29:1065-1077. 7. Marvo, S. L., S. R. King, and S. R. Jaskunas. 1983. Role of short regions of homology in intermolecular illegitimate recombination events. Proc. Natl. Acad. Sci. U.S.A. 80:2452-2456. 8. Maxam, A. M., and W. Gilbert. 1980. Sequencing end-labeled DNA with base-specific chemical cleavages. Methods Enzymol. 65:499-560. 9. Mocarski, E. S., and B. Roizman. 1981. Site-specific inversion sequence of the herpes simplex virus genome: domain and structural features. Proc. Natl. Acad. Sci. U.S.A. 78:7047-7051. 10. Mocarski, E. S., and B. Roizman. 1982. Herpesvirus-dependent amplification and inversion of cell-associated viral thymidine kinase gene flanked by viral a sequences and linked to an origin of viral DNA replication. Proc. Natl. Acad. Sci. U.S.A. 79:5626-5630. 11. Mocarski, E. S., and B. Roizman. 1982. Structure and role of the herpes simplex virus DNA termini in inversion, circularization and generation of virion DNA. Cell 31:89-97. 12. Morrison, A., and N. R. Cozzarelli. 1981. Contacts between DNA gyrase and its binding site on DNA: features of symmetry and asymmetry revealed by protection from nucleases. Proc. Natl. Acad. Sci. U.S.A. 78:1416-1420.
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13. Murchie, M.-J., and D. J. McGeoch. 1982. DNA sequence analysis of an immediate-early gene region of the herpes simplex virus type 1 genome (map coordinates 0.950 to 0.978). J. Gen. Virol. 62:1-15. 14. Rixon, F. J., and D. J. McGeoch. 1984. A 3' co-terminal family of mRNAs from the herpes simplex virus type 1 short region: two overlapping reading frames encode unrelated polypeptides one of which has a highly reiterated amino acid sequence. Nucleic Acids Res. 12:2473-2487. 15. Roizman, B. 1979. The structure and isomerization of herpes simplex virus genomes. Cell 16:481-494. 16. Stow, N. D., and E. C. McMonagle. 1983. Characterization of the TRs/IRs origin of DNA replication of herpes simplex virus type 1. Virology 130:427-438. 17. Umene, K., and L. W. Enquist. 1981. A deletion analysis of lambda hybrid phage carrying the Us region of herpes simplex virus type 1 (Patton). I. Isolation of deletion derivatives and identification of chi-likes sequences. Gene 13:251-268. 17a.Umene, K., R. J. Watson, and L. W. Enquist. 1984. Tandem repeated DNA in an intergenic region of Herpes simplex virus type 1. (Patton). Gene 30:33-39. 18. Watson, R. J., M. Sullivan, and G. F. Vande Woude. 1981. Structures of two spliced herpes simplex virus type 1 immediate-early mRNA's which map at the junctions of the unique and reiterated regions of the virus DNA S component. J. Virol. 37:431 444. 19. Watson, R. J., and G. F. Vande Woude. 1982. DNA sequence of an immediate-early gene (IE mRNA-5) of herpes simplex virus type I. Nucleic Acids Res. 10:979-991.
