A mutation in the latency-related gene of bovine herpesvirus 1 leads to impaired ocular shedding in acutely infected calves

A protein encoded by the bovine herpesvirus 1 latency-related gene interacts with specific cellular regulatory proteins, including CCAAT enhancer binding protein alpha

Following acute infection, bovine herpesvirus 1 establishes latency in sensory neurons of trigeminal ganglia (TG). Reactivation from latency occurs periodically, resulting in the shedding of infectious virus. The latency-related (LR) RNA is abundantly expressed in TG of latently infected calves, and the expression of LR proteins is necessary for dexamethasone-induced reactivation from latency. Previously published studies also identified an alternatively spliced LR transcript which is abundantly expressed in TG at 7 days after infection and has the potential to encode a novel LR fusion protein. Seven days after infection is when extensive viral gene expression is extinguished in TG and latency is established, suggesting that LR gene products influence the establishment of latency. In this study, we used a bacterial two-hybrid assay to identify cellular proteins that interact with the novel LR fusion protein. The LR fusion protein interacts with two proteins that can induce apoptosis (Bid and Cdc42) and with CCAAT enhancer binding protein alpha (C/EBP-alpha). Additional studies confirmed that the LR fusion protein interacts with human or insect C/EBP-alpha. C/EBP-alpha protein expression is induced in TG neurons of infected calves and after dexamethasone-induced reactivation from latency. Wild-type C/EBP-alpha, but not a DNA binding mutant of C/EBP-alpha, enhances plaque formation in bovine cells. We hypothesize that interactions between the LR fusion protein and C/EBP-alpha promote the establishment of latency.

Bovine herpesvirus 1 immediate-early protein (bICP0) interacts with the histone acetyltransferase p300, which stimulates productive infection and gC promoter activity

The immediate-early protein, bICP0, ofBovine herpesvirus 1(BHV-1) transactivates viral promoters and stimulates productive infection. bICP0 is expressed constitutively during productive infection, as its gene contains an immediate-early and an early promoter. Like other ICP0 homologues encoded by members of the subfamilyAlphaherpesvirinae, bICP0 contains a zinc RING finger located near its N terminus. Mutations that disrupt the bICP0 zinc RING finger impair its ability to activate transcription, stimulate productive infection, inhibit interferon-dependent transcription in certain cell types and regulate subnuclear localization. bICP0 also interacts with a cellular chromatin-remodelling enzyme, histone deacetylase 1 (HDAC1), and can relieve HDAC1-mediated transcriptional repression, suggesting that bICP0 inhibits silencing of the viral genome. In this study, it was shown that bICP0 interacted with the histone acetyltransferase p300 during productive infection and in transiently transfected cells. In addition, p300 enhanced BHV-1 productive infection and transactivated a late viral promoter (gC). In contrast, a CH3-domain deletion mutant of p300, which is a dominant-negative mutant, did not activate the gC promoter. bICP0 and p300 cooperated to activate the gC promoter, suggesting that there is a synergistic effect on promoter activation. As p300 can activate certain antiviral signalling pathways (for example, interferon), it was hypothesized that interactions between p300 and bICP0 may dampen the antiviral response following infection.

Localization of sequences within the latency-related gene of bovine herpesvirus 1 that inhibit mammalian cell growth

The latency-related (LR) RNA of bovine herpes virus 1 (BHV-1) is abundantly expressed in sensory neurons of latently infected cattle. Wild-type expression of LR gene products is required for the latency-reactivation cycle. LR gene products inhibit apoptosis, bICP0 expression, and mammalian cell growth. The cell growth inhibitory function of the LR gene maps to a 463-bp XbaI-PstI fragment. Introduction of stop codons into the XbaI-PstI fragment had no effect on inhibiting growth. Expression of a LR strand-specific transcript correlates with growth inhibition in bovine fibroblasts and mouse neuroblastoma cells.

Functional analysis of bovine herpesvirus 1 (BHV-1) genes expressed during latency

Bovine herpes virus 1 (BHV-1) establishes latency in sensory neurons of trigeminal ganglia (TG), and germinal centers of pharyngeal tonsil. Periodically BHV-1 reactivates from latency, virus is shed, and consequently virus transmission occurs. Two transcripts, the latency related (LR) RNA and ORF-E, are abundantly expressed in TG of latently infected cattle. A LR mutant strain of BHV-1 was constructed that contains stop codons near the beginning of the LR-RNA. The LR mutant virus does not express two proteins encoded by the LR gene, or reactivate from latency suggesting that LR protein expression regulates the latency-reactivation cycle. Higher levels of apoptosis occur in TG of calves infected with the LR mutant versus wild type BHV-1 indicating that the anti-apoptotic properties of the LR gene regulate the latency-reactivation cycle. The LR gene also inhibits bICP0 expression and mammalian cell growth, but these functions do not require LR protein expression. In contrast, the ability of the LR gene to inhibit apoptosis appears to require LR protein expression. A small open reading frame (ORF-E) that is located within the LR promoter is expressed in the nucleus of neuroblastoma cells. We predict that the LR gene and ORF-E regulate the BHV-1 latency-reactivation cycle.

Analysis of a bovine herpesvirus 1 recombinant virus that does not express the bICP0 protein

Bovine herpesvirus 1 (BHV-1) infected-cell protein 0 (bICP0) stimulates productive infection by activating viral gene expression. In this study, an attempt was made to construct a recombinant virus with point mutations in the C3HC4zinc RING finger of bICP0, as this domain is necessary for activating viral transcription and productive infection. A virus was identified in bovine cells that induced small clusters of infected cells resembling a small plaque. Instead of the expected mutations within the zinc RING finger, this virus contained a point mutation within the initiating ATG of bICP0, a point mutation two bases downstream from the ATG mutation and deletion of flanking plasmid sequences used for homologous recombination. The bICP0 mutant was rescued with wild-type (wt) bICP0 sequences and the bICP0-rescued virus produced wt plaques. The bICP0-rescued virus and wt BHV-1, but not the mutant, expressed the bICP0 protein during productive infection of bovine cells, suggesting that the mutant virus was a null mutant. Consequently, the mutant was designated the bICP0 null mutant. Infection of bovine cells with the bICP0 null mutant resulted in at least 100-fold lower virus titres, indicating that bICP0 protein expression is important, but not required, for virus production. When bovine cells infected with the bICP0 null mutant virus were subcultured, the cells continued to divide, but viral DNA could be detected after more than 35 passages, suggesting that the bICP0 null mutant induced a persistent-like infection in bovine cells and that it may be useful for generating additional bICP0 mutants.

Latency-related gene encoded by bovine herpesvirus 1 promotes virus growth and reactivation from latency in tonsils of infected calves

Infection of calves with bovine herpesvirus 1 (BHV-1) results in transient immunosuppression that may lead to bacterium-induced pneumonia and, occasionally, death. Although sensory neurons in the trigeminal ganglia (TG) are the primary site of BHV-1 latency, viral genomes are detected in the tonsils of latently infected calves. Dexamethasone (DEX) consistently induces reactivation from latency, and viral gene expression is detected in TG and tonsils. In sensory neurons of latently infected calves, the latency-related (LR) gene is abundantly expressed and is required for reactivation from latency. In the present study, we compared the abilities of wild-type (wt) BHV-1 and a strain with a mutation in the LR gene (the LR mutant strain) to grow in the tonsils of infected calves and reactivate from latency. Lower levels of the LR mutant virus were detected in the tonsils of acutely infected calves. LR mutant viral DNA was consistently detected by PCR in the tonsils of latently infected calves, suggesting that the establishment of a latent or persistent infection occurred. Although the LR mutant did not reactivate from latency in vivo after DEX treatment, explantation of tonsil tissue from calves latently infected with the LR mutant yielded infectious virus. Relative to wt BHV-1, the LR mutant did not induce explant-induced reactivation as efficiently. These studies indicate that the LR gene promotes virus shedding from tonsil tissue during acute infection and reactivation from latency in tonsil tissue in vivo. We suggest that incorporation of the LR gene mutation into existing modified live vaccines would prevent reactivation from latency in neural and nonneural sites and would thus prevent transmission to other animals.

Identifying critical parameters in the dynamics and control of microparasite infection using a stochastic epidemiological model

A stochastic epidemic model is presented to study infection transmission dynamics, and hence epidemic severity and disease incidence, in a closed population. The aim was to understand the relative importance of various parameters that influence the dynamics of potential epidemics, particularly when the genetic mechanisms of resistance or tolerance to infection are considered. Simulations explored the effect of varying the transmission coefficient, latent period, recovery period, mortality rate, and the period of loss of immunity on overall epidemic outcomes. The critical parameters influencing the transmission of infection, and hence disease incidence, were the transmission coefficient, the latent period, and the recovery period; the period of loss of immunity had only trivial effects. Ideally, control strategies should decrease the transmission coefficient and/or increase the latent period and/or decrease the recovery period. By equating measured traits with disease transmission parameters, the model described in this paper can be used to identify which disease resistance genes or QTL will be truly effective in helping to develop disease-resistant livestock that suffer fewer epidemics and side-effects of infection. In particular, emphases should be placed on finding genes that decrease the transmission of infection, increase the latent period, or decrease the recovery period.

Identification of a novel bovine herpesvirus 1 transcript containing a small open reading frame that is expressed in trigeminal ganglia of latently infected cattle

Bovine herpesvirus 1 (BHV-1), like other Alphaherpesvirinae subfamily members, establishes latency in sensory neurons. The latency-related (LR) RNA is abundantly expressed during latency, and expression of an LR protein is required for the latency reactivation cycle in cattle. Within LR promoter sequences, a 135-amino-acid open reading frame (ORF) was identified, ORF-E, that is antisense to the LR RNA. ORF-E is also downstream of the gene encoding the major viral transcriptional activator, bICP0. Strand-specific reverse transcription-PCR demonstrated that a transcript containing ORF-E was consistently expressed in trigeminal ganglia (TG) of latently infected calves, productively infected cultured cells, and acutely infected calves. As expected, a late transcript encoding glycoprotein C was not detected in TG of latently infected calves. The ORF-E transcript is polyadenylated and is expressed early when cultured bovine cells are productively infected. Protein coding sequences containing ORF-E were fused to green fluorescent protein (GFP) to examine the cellular localization of the putative protein. In transiently transfected mouse neuroblastoma (neuro-2A) and human neuroblastoma (SK-N-SH) cells, the ORF-E/GFP fusion protein was detected in discreet domains within the nucleus. In contrast, the ORF-E/GFP fusion protein was detected in the cytoplasm and nucleus of rabbit skin cells and bovine kidney cells. As expected, the GFP protein was expressed in the cytoplasm and nucleus of transfected cells. These studies indicate that the ORF-E transcript is consistently expressed during latency. We suggest that the ORF-E gene regulates some aspect of the latency reactivation cycle.

The latency-related gene encoded by bovine herpesvirus 1 can suppress caspase 3 and caspase 9 cleavage during productive infection

When the bovine herpesvirus 1 (BHV-1) latency-related (LR) gene is inserted into the latency-associated transcript (LAT) locus of a herpes simplex virus type 1 (HSV-1) LAT deletion mutant, high levels of spontaneous reactivation from latency and enhanced pathogenesis occur. The LR gene, but not LAT, inhibits caspase 3 cleavage during productive infection. Plasmids containing LAT or the LR gene inhibit caspase 3 activation in transiently transfected cells, suggesting productive infection blocks certain antiapoptotic properties of LAT. These studies demonstrate a correlation between the enhanced pathogenic potential of CJLAT and the LR gene inhibiting caspase 3 cleavage during productive infection.

A mutation in the latency-related gene of bovine herpesvirus 1 inhibits protein expression from open reading frame 2 and an adjacent reading frame during productive infection

The latency-related (LR) gene of bovine herpesvirus 1 (BHV-1) is abundantly expressed during latency. A mutant BHV-1 strain that contains three stop codons at the 5' terminus of the LR gene (LR mutant) does not reactivate from latency. This study demonstrates that the LR mutant does not express open reading frame 2 or an adjacent reading frame that lacks an initiating ATG (reading frame C). Since the LR mutant and wild-type BHV-1 express similar levels of LR RNA, we conclude that LR protein expression plays an important role in regulating the latency reactivation cycle in cattle.

Cloning and initial characterization of an alternatively spliced transcript encoded by the bovine herpes virus 1 latency-related gene

Bovine herpesvirus 1 (BHV-1) establishes latency in trigeminal ganglionic sensory neurons of infected cattle. The latency-related (LR) RNA is the only abundantly expressed viral transcript in sensory neurons of latently infected calves. Wild-type expression of LR gene products is required for the latency-reactivation cycle in calves. LR RNA is alternatively spliced in trigeminal ganglia (TG) after infection of calves, suggesting that these alternatively spliced transcripts encode novel factors that regulate specific steps during latency. To begin testing whether these alternatively spliced transcripts have novel functions, the authors cloned a full-length cDNA identified in TG of calves at 7 days post infection (dpi) and compared the functions of this cDNA to the intact LR gene. As a result of splicing, the 7 dpi cDNA contains a novel open reading (ORF) comprised of OFR-2 fused to ORF-1. Overexpression of the 7 dpi cDNA inhibited the BHV-1 immediate-early transcription unit 1 (IEtu1) promoter and the herpes simplex virus type 1 ICP0 promoter. Conversely, the 7 dpi cDNA stimulated the LR promoter in transiently transfected cells. A plasmid containing the LR gene had little effect on IEtu1 or LR promoter activity, indicating that the 7 dpi cDNA has novel functions.

Genome of bovine herpesvirus 5

Here we present the complete genomic sequence of bovine herpesvirus 5 (BHV-5), an alphaherpesvirus responsible for fatal meningoencephalitis in cattle. The 138390-bp genome encodes 70 putative proteins and resembles the alpha2 subgroup of herpesviruses in genomic organization and gene content. BHV-5 is very similar to BHV-1, the etiological agent of infectious bovine rhinotracheitis, as reflected by the high level of amino acid identity in their protein repertoires (average, 82%). The highest similarity to BHV-1 products (>or=95% amino acid identity) is found in proteins involved in viral DNA replication and processing (UL5, UL15, UL29, and UL39) and in virion proteins (UL14, UL19, UL48, and US6). Among the least conserved ( Collapse

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MESH Headings

• Amino Acid Sequence
• Base Sequence
• Genes, Immediate-Early
• Genome, Viral
• Herpesvirus 5, Bovine/genetics
• Molecular Sequence Data
• Promoter Regions, Genetic
• Repetitive Sequences, Nucleic Acid
• Virus Latency/genetics

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Affiliation(s)

G Delhon Plum Island Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture, Greenport, New York 11944, USA
M P Moraes
Z Lu
C L Afonso
E F Flores
R Weiblen
G F Kutish
D L Rock

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Infection of cattle with a bovine herpesvirus 1 strain that contains a mutation in the latency-related gene leads to increased apoptosis in trigeminal ganglia during the transition from acute infection to latency

Bovine herpesvirus 1 (BHV-1) is an important pathogen of cattle and infection is usually initiated via the ocular or nasal cavity. After acute infection, the primary site for BHV-1 latency is sensory neurons in the trigeminal ganglia (TG). Reactivation from latency occurs sporadically, resulting in virus shedding and transmission to uninfected cattle. The only abundant viral transcript expressed during latency is the latency-related (LR) RNA. An LR mutant was constructed by inserting three stop codons near the beginning of the LR RNA. This mutant grows to wild-type (wt) efficiency in bovine kidney cells and in the nasal cavity of acutely infected calves. However, shedding of infectious virus from the eye and TG was dramatically reduced in calves infected with the LR mutant. Calves latently infected with the LR mutant do not reactivate after dexamethasone treatment. In contrast, all calves latently infected with wt BHV-1 or the LR rescued mutant reactivate from latency after dexamethasone treatment. In the present study, we compared the frequency of apoptosis in calves infected with the LR mutant to calves infected with wt BHV-1 because LR gene products inhibit apoptosis in transiently transfected cells. A sensitive TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) assay and an antibody that detects cleaved caspase-3 were used to identify apoptotic cells in TG. Both assays demonstrated that calves infected with the LR mutant for 14 days had higher levels of apoptosis in TG compared to calves infected with wt BHV-1 or to mock-infected calves. Viral gene expression, except for the LR gene, is extinguished by 14 days after infection, and thus this time frame is operationally defined as the establishment of latency. Real-time PCR analysis indicated that lower levels of viral DNA were present in the TG of calves infected with the LR mutant throughout acute infection. Taken together, these results suggest that the antiapoptotic properties of the LR gene play an important role during the establishment of latency.

Stimulation of bovine herpesvirus-1 productive infection by the adenovirus E1A gene and a cell cycle regulatory gene, E2F-4

Identifying cellular genes that promote bovine herpesvirus-1 (BHV-1) productive infection is important, as BHV-1 is a significant bovine pathogen. Previous studies demonstrated that BHV-1 DNA is not very infectious unless cotransfected with a plasmid expressing bICP0, a viral protein that stimulates expression of all classes of viral promoters. Based on these and other studies, we hypothesize that the ability of bICP0 to interact with and modify the function of cellular proteins stimulates virus transcription. If this prediction is correct, cellular proteins that activate virus transcription could, in part, substitute for bICP0 functions. The adenovirus E1A gene and bICP0 encode proteins that are potent activators of viral gene expression, they do not specifically bind DNA and both proteins interact with chromatin-remodelling enzymes. Because of these functional similarities, E1A was tested initially to see if it could stimulate BHV-1 productive infection. E1A consistently stimulates BHV-1 productive infection, but not as efficiently as bICP0. The ability of E1A to bind Rb family members plays a role in stimulating productive infection, suggesting that E2F family members activate productive infection. E2F-4, but not E2F-1, E2F-2 or E2F-5, activates productive infection with similar efficiency as E1A. Next, E2F family members were examined for their ability to activate the BHV-1 immediate-early (IE) transcription unit 1 (IEtu1) promoter, as it regulates IE expression of bICP0 and bICP4. E2F-1 and E2F-2 strongly activate the IEtu1 promoter, but not a BHV-1 IEtu2 promoter or a herpes simplex virus type 1 ICP0 promoter construct. These studies suggest that E2F family members can stimulate BHV-1 productive infection.

Herpes simplex virus type 1 and bovine herpesvirus 1 latency

Primary infection by herpes simplex virus type 1 (HSV-1) can cause clinical symptoms in the peripheral and central nervous system, upper respiratory tract, and gastrointestinal tract. Recurrent ocular shedding leads to corneal scarring that can progress to vision loss. Consequently, HSV-1 is the leading cause of corneal blindness due to an infectious agent. Bovine herpesvirus 1 (BHV-1) has similar biological properties to HSV-1 and is a significant health concern to the cattle industry. Latency of BHV-1 and HSV-1 is established in sensory neurons of trigeminal ganglia, but latency can be interrupted periodically, leading to reactivation from latency and spread of infectious virus. The ability of HSV-1 and BHV-1 to reactivate from latency leads to virus transmission and can lead to recurrent disease in individuals latently infected with HSV-1. During latency, the only abundant HSV-1 RNA expressed is the latency-associated transcript (LAT). In latently infected cattle, the latency-related (LR) RNA is the only abundant transcript that is expressed. LAT and LR RNA are antisense to ICP0 or bICP0, viral genes that are crucial for productive infection, suggesting that LAT and LR RNA interfere with productive infection by inhibiting ICP0 or bICP0 expression. Numerous studies have concluded that LAT expression is important for the latency-reactivation cycle in animal models. The LR gene has recently been demonstrated to be required for the latency-reactivation cycle in cattle. Several recent studies have demonstrated that LAT and the LR gene inhibit apoptosis (programmed cell death) in trigeminal ganglia of infected animals and transiently transfected cells. The antiapoptotic properties of LAT map to the same sequences that are necessary for promoting reactivation from latency. This review summarizes our current knowledge of factors regulating the latency-reactivation cycle of HSV-1 and BHV-1.

The latency-related gene of bovine herpesvirus-1 can inhibit the ability of bICP0 to activate productive infection

Transfection of bovine cells with bovine herpesvirus-1 genomic DNA yields low levels of infectious virus. Cotransfection with the bICP0 gene enhances productive infection and virus yield because bICP0 can activate viral gene expression. Since the latency-related (LR) gene overlaps and is antisense to bICP0, the effects of LR gene products on productive infection were tested. The intact LR gene inhibited productive infection in a dose-dependent fashion but LR protein expression was not required. Further studies indicated that LR gene sequences near the 3' terminus of the LR RNA are necessary for inhibiting productive infection. When cotransfected with the bICP0 gene, the LR gene inhibited bICP0 RNA and protein expression in transiently transfected cells. Taken together, these results suggest that abundant LR RNA expression in sensory neurons is one factor that has the potential to inhibit productive infection and consequently promote the establishment and maintenance of latency.

A mutation in the latency-related gene of bovine herpesvirus 1 disrupts the latency reactivation cycle in calves

Bovine herpesvirus 1 (BHV-1) is an important pathogen of cattle, and infection is usually initiated via the ocular or nasal cavity. Following acute infection, the primary site for BHV-1 latency is the sensory neuron. Reactivation from latency occurs sporadically, resulting in virus shedding and transmission to uninfected cattle. The only abundant viral transcript expressed during latency is the latency-related (LR) RNA, suggesting that it mediates some aspect of latency. An LR mutant was constructed by inserting three stop codons near the beginning of the LR-RNA, suggesting that expression of LR proteins would be altered. The LR mutant grew with wild-type (wt) efficiency in bovine kidney cells (MDBK). When calves were infected with the LR mutant, a dramatic decrease (3 to 4 logs) in ocular, but not nasal, viral shedding occurred during acute infection relative to the wt or the LR-rescued virus (M. Inman, L. Lovato, A. Doster, and C. Jones, J. Virol. 75:8507-8515, 2001). In this study, we examined the latency reactivation cycle in calves infected with the LR mutant and compared these results to those from calves infected with wt BHV-1 or the LR-rescued virus. During acute infection, lower levels of infectious virus were detected in trigeminal ganglion homogenates from calves infected with the LR mutant. As judged by in situ hybridization, BHV-1-positive neurons were detected in trigeminal ganglia of calves infected with the wt but not the LR mutant. Although LR-RNA was detected by reverse transcription-PCR in calves latently infected with the LR mutant, a semiquantitative PCR analysis revealed that lower levels of viral DNA were present in trigeminal ganglia of calves infected with the LR mutant. Dexamethasone treatment of calves latently infected with wt BHV-1 or the LR-rescued virus, but not the LR mutant, consistently induced reactivation from latency, as judged by shedding of infectious virus from the nose or eyes and increases in BHV-1-specific antibodies. In summary, this study demonstrates that wt expression of LR gene products plays an important role in the latency reactivation cycle of BHV-1 in cattle.

A gene capable of blocking apoptosis can substitute for the herpes simplex virus type 1 latency-associated transcript gene and restore wild-type reactivation levels

After ocular herpes simplex virus type 1 (HSV-1) infection, the virus travels up axons and establishes a lifelong latent infection in neurons of the trigeminal ganglia. LAT (latency-associated transcript), the only known viral gene abundantly transcribed during HSV-1 neuronal latency, is required for high levels of reactivation. The LAT function responsible for this reactivation phenotype is not known. Recently, we showed that LAT can block programmed cell death (apoptosis) in neurons of the trigeminal ganglion in vivo and in tissue culture cells in vitro (G.-C. Perng et al., Science 287:1500-1503, 2000; M. Inman et al., J. Virol. 75:3636-3646, 2001). Consequently, we proposed that this antiapoptosis function may be a key to the mechanism by which LAT enhances reactivation. To study this further, we constructed a recombinant HSV-1 virus in which the HSV-1 LAT gene was replaced by an alternate antiapoptosis gene. We used the bovine herpes virus 1 (BHV-1) latency-related (LR) gene, which was previously shown to have antiapoptosis activity, for this purpose. The resulting chimeric virus, designated CJLAT, contains two complete copies of the BHV-1 LR gene (one in each viral long repeat) in place of the normal two copies of the HSV-1 LAT, on an otherwise wild-type HSV-1 strain McKrae genomic background. We report here that in both rabbits and mice reactivation of CJLAT was significantly greater than the LAT null mutant dLAT2903 (P < 0.0004 and P = 0.001, respectively) and was at least as efficient as wild-type McKrae. This strongly suggests that a BHV-1 LR gene function was able to efficiently substitute for an HSV-1 LAT gene function involved in reactivation. Although replication of CJLAT in rabbits and mice was similar to that of wild-type McKrae, CJLAT killed more mice during acute infection and caused more corneal scarring in latently infected rabbits. This suggested that the BHV-1 LR gene and the HSV-1 LAT gene are not functionally identical. However, LR and LAT both have antiapoptosis activity. These studies therefore strongly support the hypothesis that replacing LAT with an antiapoptosis gene restores the wild-type reactivation phenotype to a LAT null mutant of HSV-1 McKrae.