Virus-induced modification of the host cell is required for expression of the bacterial chloramphenicol acetyltransferase gene controlled by a late herpes simplex virus promoter (VP5)

Regulation of a human cytomegalovirus immediate-early gene (US3) by a silencer-enhancer combination

The US3 open reading frame of human cytomegalovirus (HCMV) is transcribed at immediate-early (IE) times after infection. Upstream of the US3 promoter, between -84 and -259 bp relative to the transcription start site, there are five copies of an 18-bp repeat, referred to as 5R2. Between -340 and -560 bp there are seven copies of a 10-bp dyad repeat, referred to as 7R1. We investigated the roles of these repeats in transcription from the US3 promoter in human foreskin fibroblast or HeLa cells. In transient transfection assays, the region containing 5R2 up-regulated transcription and was responsive to the p65 subunit of NF-kappa B. The DNA region containing 7R1 down-regulated transcription from either the US3 promoter or a heterologous promoter in a position- and orientation-independent manner. Mutational analysis and transient transfections indicated that DNA containing the 10-bp dyad or one-half of the dyad was sufficient to cause repression of downstream gene expression. DNA probes containing one or more copies of the pentanucleotide sequence TGTCG specifically bound cellular proteins, as demonstrated by electrophoretic mobility shift assays and cold-competition electrophoretic mobility shift assays. Two different DNA-protein complexes were detected with DNA probes containing one or two copies of the pentanucleotide. In HCMV-infected cell nuclear extracts, one of the DNA-protein complexes was present in amounts inversely proportional to the amount of US3 transcription. Its formation was affected by dephosphorylation of the DNA-binding protein(s). Transient dephosphorylation of the cellular repressor protein may occur during HCMV infection. Repression of US3 transcription may relate to the number of pentanucleotides and the cellular proteins that bind to it. Twenty-one copies of a TRTCG motif (R = purine) were found clustered upstream of the US3 gene and also in the modulator upstream of the HCMV IE1 and IE2 genes.

Herpes simplex virus recombination vectors designed to allow insertion of modified promoters into transcriptionally "neutral" segments of the viral genome

The use of recombinant viruses has been essential in investigation of the biology of herpes simplex virus (HSV). In this communication we describe a number of viral recombination vectors that we have generated for use in promoter structure/function analysis within the context of the HSV-1 genome. We have utilized two regions of the HSV genome that contain genes nonessential for replication in cultured cells--the glycoprotein C (gC or UL44) locus in the UL of the genome and the area encompassing the promoter and 5' portion of the latency associated transcript (LAT) within the RL factual influence on promoters due to the site of insertion. Two different kinetic promoters were analyzed, those controlling expression of the gamma UL 38 and the beta dUTPase genes, in both loci. All constructs tested displayed reporter gene mRNA expression with expected kinetics, and we conclude that there are no neighboring cryptic promoter elements that could interfere with expression studies using the vectors described.

A cell-free recombination system for site-specific integration of multigenic shuttle plasmids into the herpes simplex virus type 1 genome

This report describes a novel method for complementation studies of defective herpes simplex virus (HSV) genes. Viral test gene and nonviral reporter gene cassettes were rapidly integrated into the HSV genome in a site-specific and reversible manner by using the P1 phage-based Cre-lox recombination system. Shuttle plasmids contained a functional loxP recombination site, an expressible form of the bacterial lacZ gene, and a copy of the wild-type glycoprotein B (gB) gene or double mutant gB allele containing both a temperature-sensitive (ts) mutation and a syncytium (syn)-forming mutation. A recipient viral genome, K delta T::lox1, was constructed from the HSV type 1 (syn) gB-deficient mutant virus, K delta T, by marker transfer of the loxP recombination site into the viral thymidine kinase locus. Shuttle plasmids of up to 12.9 kb in length were recombined with high efficiency (11 to 20%) into the K delta T::lox1 genome in cell-free, Cre-mediated recombination reactions. Expression of a functional wild-type or double mutant gB polypeptide complemented the nonfunctional polypeptide expressed from the deleted, normal gB locus and allowed production of either wild-type or Syn- plaques on Vero cells. The latter recombinant virus was also ts for growth. The ability to express viral genes from plasmids which can be shuttled into and out of the HSV genome in cell-free recombination reactions makes this a powerful method for performing genetic studies of the biologic properties of viral gene products.

Transactivation of the major capsid protein gene of herpes simplex virus type 1 requires a cellular transcription factor

The purpose of this investigation was to identify and characterize the regulatory elements involved in the transcriptional activation of the beta gamma (leaky-late or gamma 1) genes of herpes simplex virus type 1 (HSV-1) by using the major capsid protein (VP5 or ICP5) gene as model. Gel mobility shift assays with nuclear extracts from uninfected and infected HeLa cells enabled us to identify two major protein-DNA complexes involving the VP5 promoter. The mobilities of these two complexes remained unaltered, and no unique complexes were observed when infected cell nuclear extracts were used. DNase I and orthophenanthroline-Cu+ footprint analyses revealed that the two complexes involve a single binding site, GGCCATCTTGAA, located between -64 and -75 bp relative to the VP5 cap site. To determine the function of this leaky-late binding site (LBS) in VP5 gene activation, we tested the effect of mutations in this region by using transient expression of a cis-linked chloramphenicol acetyltransferase gene. Deletion of the above sequence resulted in a seven- to eightfold reduction in the level of transactivation of the chloramphenicol acetyltransferase gene by superinfection with HSV-1 or by cotransfection of HSV-1 immediate-early genes. From these results, we conclude that the LBS sequence and a cellular factor(s) are involved in the transactivation of the VP5 gene. A search of published gene sequences revealed that sequences related to the LBS exist in a number of other HSV-1, cytomegalovirus, retrovirus, and cellular promoters. Sequence homologies of binding sites and results of unpublished competition binding studies suggest that this leaky-late binding factor may be related to, or the same as, a ubiquitous cellular transcriptional factor called YY1 or common factor-1 (also known as NF-E1, delta, and UCRBP).

A herpesvirus regulatory protein appears to act post-transcriptionally by affecting mRNA processing

Post-transcriptional control mechanisms play an important role in regulating gene expression for a number of viruses, especially in the regulation of late gene products. In this study we have investigated the mode of action of ICP27, an immediate-early regulatory protein of herpes simplex virus 1 (HSV-1) required for late gene expression. Transfection experiments have demonstrated that ICP27 can activate or repress expression depending on the target gene. Here, we show that the regulatory activity of ICP27 is independent of the target gene promoter sequences but, instead, depends on the presence of different mRNA processing signals. The activation function correlated with different polyadenylation sites, whereas the repressor function correlated with the presence of introns either 5' or 3' to the target gene-coding sequences. Poly(A)+ RNA levels were increased by ICP27 in transfections with a target gene having only an AATAAA recognition signal but no G/U box within the usual distance. In contrast, in the presence of ICP27, spliced target mRNAs were decreased 5- to 10-fold in transfections with target genes containing a 5' or 3' intron. These results suggest that this essential HSV-1 regulatory protein acts post-transcriptionally to affect mRNA processing and point to possible interactions between splicing and polyadenylation factors.

Functional analysis of the true late human cytomegalovirus pp28 upstream promoter: cis-acting elements and viral trans-acting proteins necessary for promoter activation

As a model for analyzing the regulation of human cytomegalovirus late genes, we investigated the 28-kDa phosphoprotein (pp28) gene region. Transcripts of 1.6 and 1.3 kb were expressed in wild-type human cytomegalovirus-infected cells but not in cells infected with a DNA-negative temperature-sensitive mutant (ts66), indicating that DNA replication is absolutely required for pp28 gene expression. Transient promoter activation studies revealed that the pp28 gene region upstream promoter (pp28US) functioned early when expressed independently of the viral genome. However, the promoter was not efficiently activated by immediate-early (IE) proteins but was activated equally well by both wild-type virus and ts66. Deletion analysis of the pp28US promoter indicated that sequences upstream of the CAP site between -107 and -32 were required for activation of the pp28 promoter. Within that region exist a 10-bp sequence at -90 (AGTGAT CGTG) and its inverted repeat at -32 which positively influence pp28 promoter function. Therefore, in the case of the pp28US promoter, viral proteins interact through discrete sequences to facilitate late gene expression.

Herpes simplex virus type 1 latency-associated transcription unit promotes anatomical site-dependent establishment and reactivation from latency

Defined herpes simplex virus type 1 (HSV-1) mutants KOS/1 and KOS/62 (positive and negative, respectively, for latency-associated transcripts [LATs]) express the Escherichia coli beta-galactosidase (beta-Gal) gene during latency. These mutants were employed to assess the functions of the latency-associated transcription unit on establishment and maintenance of and reactivation from the latent state. It was found that in the trigeminal ganglia, the frequencies of hyperthermia-induced reactivation of KOS/62 and an additional LATs- mutant (KOS/29) were reduced by at least 80%. Quantification of latently infected neurons expressing the beta-Gal gene revealed that the LATs- mutant KOS/62 established approximately 80% fewer latent infections in the trigeminal ganglia than did KOS/1 (LATs+). This reduction in establishment which is evident in the trigeminal ganglia could account for the reduced frequency of reactivation from this site. In striking contrast, both LATs- mutants reactivated with wild-type frequencies from lumbosacral ganglia. Quantification of beta-Gal-positive neurons at this site revealed that KOS/62 established as many as or more latent infections than the LATs+ virus, KOS/1. Colocalization of HSV antigen and beta-Gal suggested that the decreased establishment by LATs- mutants in trigeminal ganglia was the result of inefficient viral shutoff. Thus, one function of the HSV-1 LATs transcription unit is to promote the establishment of latency in trigeminal but not lumbosacral ganglia. Such a function may be relevant to understanding the distinct clinical recurrent disease patterns of HSV-1 and HSV-2.

Analysis of the herpes simplex virus type 1 promoter controlling the expression of UL38, a true late gene involved in capsid assembly

The cistrons encoding the herpes simplex virus type 1 (HSV-1) UL37 and UL38 genes are adjacent to one another but are transcribed from opposite strands of the viral DNA. The UL37 gene encodes a 1,123-amino-acid protein of unknown function, while the 465-amino-acid UL38 protein is involved in capsid assembly. Previous work from our laboratory indicated that the transcripts encoding these proteins are expressed with significantly different kinetics in productive infection. In the present communication we confirm the kinetic classes and precisely map the cap sites of the UL37 and UL38 mRNAs. A bifunctional reporter gene vector was used to demonstrate that divergent promoters control the expression of these reporter genes in trans-activation assays. The UL38 promoter is functionally separable from that controlling UL37 in a recombinant virus. We used deletion analysis to demonstrate that as few as 29 bases 5' of the mRNA cap site are adequate for full activity of the UL38 promoter in trans-activation assays. Finally, we analyzed the protein-binding properties of the UL38 promoter; several sites that form complexes containing ICP4, with clear homology to those identified in the HSV-1 gamma 42 promoter, are present. Thus, in general, the properties of this promoter are quite similar to those of other gamma promoters.

Transcriptional analysis of the eight-kilobase mRNA encoding the major capsid protein of human cytomegalovirus

The 8-kilobase mRNA coding for the major capsid protein (MCP) of human cytomegalovirus was precisely mapped. Two 5' ends of the transcript were located within HindIII fragment a, 29 and 34 base pairs, respectively, downstream of the sequence TATTAGA. The 3' end was localized within HindIII fragment b of the viral genome. The MCP transcript was synthesized at late times after infection and was not detected before viral DNA replication. In addition, the MCP promoter region could be identified, which strongly responded to viral trans activation at early and late times after infection in a transient expression assay.

Regulation and cell-type-specific activity of a promoter located upstream of the latency-associated transcript of herpes simplex virus type 1

To identify promoter regions which control expression of the latency-associated transcript (LAT) of herpes simplex virus type 1 (HSV-1), we constructed a series of recombinant vectors in which various sequences upstream of LAT were linked to the chloramphenicol acetyltransferase gene and tested for expression efficiency by transfection into tissue culture cells. In HeLa cells no activity was observed from the region (-250 to +201) immediately surrounding the nominal 5' end of LAT, but high levels of activity were observed by using different fragments within the region -1267 to -594. This promoter activity was largely contained within the 140-base-pair region from -797 to -658 and was 20- to 50-fold stronger than typical HSV delayed-early promoters and at least as strong as the activity from the simian virus 40 (SV40) enhancer-promoter region or the HSV immediate-early 110,000-Mr (IE110K) promoter region. In human neuroblastoma cells (IMR-32), there was a dramatic switch in relative activities in favor of the LAT promoter, so that it was 45- and 200-fold stronger than the IE110K and SV40 constructs, respectively. Furthermore, optimal activity in the neuroblastoma cells required sequences within the region -1267 to -797. This region had little effect on activity in HeLa cells. We also show that the LAT promoter activity was very efficiently repressed by the IE175K protein. From internal deletion analysis, the site of repression was located within a 55-base-pair region just downstream of a potential TATA box. This region exhibited a high degree of homology with the IE175K cap site and may be a binding site for the IE175K protein.

The regions important for the activator and repressor functions of herpes simplex virus type 1 alpha protein ICP27 map to the C-terminal half of the molecule

The herpes simplex virus type 1 (HSV-1) alpha or immediate-early proteins ICP4 (IE175), ICP0 (IE110), and ICP27 (IE63) are trans-acting proteins which affect HSV-1 gene expression. We previously showed that ICP27 in combination with ICP4 and ICP0 could act as a repressor or an activator in transfection assays, depending on the target gene (R. E. Sekulovich, K. Leary, and R. M. Sandri-Goldin, J. Virol. 62:4510-4522, 1988). To investigate the regions of the ICP27 protein which specify these functions, we constructed a series of in-frame insertion and deletion mutants in the ICP27 gene. These mutants were analyzed in transient expression assays for the ability to repress or to activate two different target genes. The target plasmids used consisted of the promoter regions from the HSV-1 beta or early gene which encodes thymidine kinase and from the beta-gamma or leaky late gene. VP5, which encodes the major capsid protein, each fused to the chloramphenicol acetyltransferase gene. Our previous studies showed that induction of pTK-CAT expression by ICP4 and ICP0 was repressed by ICP27, whereas the stimulation of pVP5-CAT expression seen with ICP4 and ICP0 was significantly increased when ICP27 was also added. In this study, a series of transfection assays was performed with each of the ICP27 mutant plasmids in combination with plasmids containing the ICP4 and ICP0 genes with each target. The results of these experiments showed that mutants containing insertions or deletions in the region from amino acids 262 to 406 in the carboxy-terminal half of the protein were unable to stimulate expression of pVP5-CAT but were able to repress induction of pTK-CAT activity by ICP4 and ICP0. Mutants in the carboxy-terminal 78 amino acids lost both activities; that is, these mutants did not show repression of pTK-CAT activity or stimulation of pVP5-CAT activity, whereas mutants in the hydrophilic amino-terminal half of ICP27 were able to perform both functions. These results show that the carboxy-terminal half of ICP27 is important for the activation and repression functions. Furthermore, the carboxy-terminal 62 amino acids are required for the repressor activity, because mutants with this region intact were able to repress. Analysis of the DNA sequence showed that there are a number of cysteine and histidine residues encoded by this region which have some similarity to zinc finger metal-binding regions found in other eucaryotic regulatory proteins. These results suggest that the structural integrity of this region is important for the function of ICP27.

Herpes simplex virus neurovirulence and productive infection of neural cells is associated with a function which maps between 0.82 and 0.832 map units on the HSV genome

A herpes simplex virus (HSV) intertypic recombinant (RE6) has been shown to be completely and specifically non-neurovirulent in mice. Direct intracranial inoculation of 10(8) PFU of RE6 does not result in a lethal encephalitis. Neurovirulent recombinant viruses were generated by cotransfection of RE6 DNA with DNA fragments cloned from the pathogenic HSV-1 strain 17 syn+. It was found that a 1.6-kb fragment mapping between 0.82-0.832 m.u. could restore the neurovirulent phenotype. Recombinants which incorporated at least part of this fragment were at least 100,000-fold more neurovirulent than RE6. The recombinants displayed a greatly enhanced capacity to replicate in mouse brain in vivo, but did not display enhanced replication over that of RE6 in cultured mouse cells at 38.5 degrees. Immunohistochemical analysis of infected mouse brain tissue revealed that the permissive host cell range of the recombinants was dramatically altered from that of RE6. While antigen positive cells were extremely rare in mouse brain tissue infected with RE6, the neurovirulent recombinants produced antigens in many cell types including neurons. Thus, wild-type HSV-1 sequences mapping between 0.82-0.832 m.u. can donate a highly neurovirulent phenotype to RE6.

Herpes simplex virus alpha protein ICP27 possesses separable positive and negative regulatory activities

The HSV-1 alpha (immediate-early) protein ICP27 expressed in transfected cells can activate the expression of certain HSV-1 promoters as well as inhibit the transactivated expression of others. We constructed a set of plasmids encoding mutant ICP27 molecules truncated at their carboxyl termini and used transfection assays to determine the functional properties of the mutant proteins. A polypeptide containing the amino-terminal 263 amino acid residues of ICP27 retained partial ability to activate gene expression but was unable to inhibit transactivation. Mutant proteins possessing 406 or 504 amino acids of ICP27 were unable to activate gene expression but retained full ability to inhibit transactivation. These results define two separable regulatory activities of ICP27, one positive and one negative, which can modulate gene expression in transfected cells. Immunoblot and immunofluorescence experiments were used to study the immunological reactivities and intracellular localizations of the mutant proteins. All proteins possessing the amino-terminal 263 amino acids of ICP27 reacted with an ICP27-specific monoclonal antibody and were localized to the cell nucleus. The mutant proteins, however, exhibited a number of phenotypes with regard to intranuclear localization. A mutant possessing 504 residues of ICP27 was similar to the wild-type protein in apparently localizing to all regions of the nucleus. A mutant containing 406 residues of ICP27, on the other hand, was mostly excluded from the nucleolar regions, while a 263-residue mutant was localized predominantly in the nucleoli. Thus, some aspect of ICP27 structure or function can dramatically affect its intranuclear distribution.

Herpes simplex virus alpha protein ICP27 can inhibit or augment viral gene transactivation

Three of the five alpha (immediate early) gene products of herpes simplex virus, infected cell proteins (ICPs) 4, 0, and 27 play a role in the control of expression of viral beta (delayed-early) and gamma (late) genes. We report here that ICP27 can inhibit or augment the individual or combined abilities of ICP4 and ICP0 to stimulate expression of chimeric genes containing viral gene promoters in a transient expression system. The specific effect of ICP27 was dependent on the viral gene promoter in the chimeric gene. ICP27 inhibited the ability of ICP4 and ICP0 to activate some beta gene promoters but augmented their ability to activate other beta or gamma 1 gene promoters when they were used in the target genes. Activation of the target genes by adenovirus E1A was not affected by ICP27 under the same conditions. ICP27 also repressed the ability of ICP0 to stimulate expression of a chimeric gene containing an alpha gene promoter. Insertion of a termination codon in the middle of the ICP27 coding region severely reduced the inhibitory effect of the plasmid, indicating that this activity requires expression of functional ICP27 polypeptide. This report focuses on the ICP27 activity that negatively regulates ICP4 transactivation of a chimeric gene containing the upstream sequences of the HSV beta gene ICP8. ICP27 decreased the level of mRNA initiated at the transcriptional start site of the ICP8 gene. The level of expression of the ICP4 gene was not changed by ICP27 but an alteration in the electrophoretic mobility of ICP4 expressed was observed. The modulatory effect of ICP27 on HSV transactivators may control the progress of the lytic cycle or provide a balance that varies in different cell types to affect whether lytic or latent infection ensues.

Transcriptional activation is not responsible for increased levels of autonomously expressed simian virus 40 T-antigen in herpes simplex virus-infected cells

Herpes simplex virus type 1 (HSV-1) superinfection of CV-1 cells weakly transactivated a plasmid-borne metallothionein 1 (MT-1) promoter, but activated the expression of a marker gene controlled by an authentic HSV-1 promoter to a high level. In contrast, CMT-3 cells, which are CV-1 cells stably transformed with the simian virus 40 (SV40) large T-antigen (T-Ag) gene controlled by the MT-1 promoter, contained high levels of T-Ag following HSV-1 superinfection, but only if cells were preincubated in the presence of heavy-metal ions. This T-Ag was functional in that it could mediate the increase in copy number of a marker plasmid containing the SV40 origin of DNA replication. Pulse and continuous labeling of preinduced CMT-3 cells showed that T-Ag expression was not induced by HSV-1; but rather, HSV-1 superinfection resulted in the stabilization of pre-existing protein.

Regulation of cellular genes transduced by herpes simplex virus

Previous studies demonstrated that the rabbit beta-globin gene is transcribed from its own promoter and regulated as a herpes simplex virus (HSV) early gene following insertion into the early HSV thymidine kinase gene in the intact viral genome (J. R. Smiley, C. Smibert, and R. D. Everrett, J. Virol. 61:2368-2377, 1987). We report here that the beta-globin promoter remained under early control after insertion into the late HSV gene encoding glycoprotein C. On the basis of these findings, we concluded that the beta-globin promoter is functionally equivalent to an HSV early-control region. We found that a transduced human alpha-globin gene was also regulated as an early HSV gene, while two linked Alu elements mimicked the behavior of HSV late genes. These results demonstrate that certain aspects of HSV temporal regulation can be duplicated by cellular elements and provide strong support for the hypothesis that the regulation of HSV gene expression can occur through mechanisms that do not rely on recognition of virus-specific temporal control signals.

Transcriptional activation with concurrent or nonconcurrent template replication has differential effects on transient expression from herpes simplex virus promoters

We have used two methods to induce template replication in order to assess the effect on expression of marker genes controlled by herpes simplex virus type 1 (HSV-1) promoters. One method used the HSV-1 origin of DNA replication from the short repeat region of the viral genome (HSV-1 oris), and allowed simultaneous replication and transcriptional activation of the plasmid-borne template. The other, using the simian virus 40 origin of replication (SV40 ori) allowed plasmid template replication prior to activation of transcription by HSV-1 infection. The two regimes had markedly different effects upon the levels of reporter gene activity induced by HSV-1 superinfection. Replication of reporter plasmids using the SV40 ori yielded levels of reporter gene activity proportional to plasmid copy number when cells were superinfected with HSV-1. In contrast, our results indicated that sequences containing, or in close proximity to, the HSV-1 oris in the reporter plasmid had a significant inhibitory effect on expression from all viral promoters whether or not the plasmid was allowed to replicate. Still, the early (beta) promoter-controlled reporter enzyme activity declined at late times while that controlled by the strict late (gamma) promoter was significantly higher following HSV-1 oris-mediated template replication.

The role of viral and cellular nuclear proteins in herpes simplex virus replication

Following infection of cells by herpes simplex virus, the cell nucleus is subverted for transcription and replication of the viral genome and assembly of progeny nucleocapsids. The transition from host to viral transcription involves viral proteins that influence the ability of the cellular RNA polymerase II to transcribe a series of viral genes. The regulation of RNA polymerase II activity by viral gene products seems to occur by several different mechanisms: (1) viral proteins complex with cellular proteins and alter their transcription-promoting activity (e.g., alpha TIF), (2) viral proteins bind to specific DNA sequences and alter transcription (e.g., ICP4), and (3) viral proteins affect the posttranslational modification of viral or cellular transcriptional regulatory proteins (e.g., possibly ICP27). Thus, HSV may utilize several different approaches to influence the ability of host-cell RNA polymerase II to transcribe viral genes. Although it is known that viral transcription uses the host-cell polymerase II, it is not known whether viral infection causes a change in the structural elements of the nucleus that promote transcription. In contrast, HSV encodes a new DNA polymerase and accessory proteins that complex with and reorganize cellular proteins to form new structures where viral DNA replication takes place. HSV may encode a large number of DNA replication proteins, including a new polymerase, because it replicates in resting cells where these cellular gene products would never be expressed. However, it imitates the host cell in that it localizes viral DNA replication proteins to discrete compartments of the nucleus where viral DNA synthesis takes place. Furthermore, there is evidence that at least one specific viral gene protein can play a role in organizing the assembly of the DNA replication structures. Further work in this system may determine whether assembly of these structures is essential for efficient viral DNA replication and if so, why assembly of these structures is necessary. Thus, the study of the localization and assembly of HSV DNA replication proteins provides a system to examine the mechanisms involved in morphogenesis of the cell nucleus. Therefore, several critical principles are apparent from these discussions of the metabolism of HSV transcription and DNA replication. First, there are many ways in which the activity of RNA polymerase II can be regulated, and HSV proteins exploit several of these in controlling the transcription of a single DNA molecule. Second, the interplay of these multiple regulatory pathways is likely to control the progress of the lytic cycle and may play a role in determining the lytic versus latent infection decision.(ABSTRACT TRUNCATED AT 400 WORDS)

The herpes simplex virus type 1 alpha protein ICP27 can act as a trans-repressor or a trans-activator in combination with ICP4 and ICP0

The herpes simplex virus type 1 (HSV-1) alpha proteins ICP4, ICP0, and ICP27 are trans-acting proteins which affect HSV-1 gene expression. To investigate potential interactions between these alpha products and to determine the specificity of action of the alpha proteins in combination with each other compared with their activities individually, we performed a series of transient-expression assays. In these assays we used plasmids containing the alpha genes encoding ICP4, ICP0, and ICP27 either singly or in combination as effectors and HSV-1 genes of different kinetic classes and heterologous genes as targets. The HSV-1 targets consisted of promoter-regulatory domains from alpha (ICP0 and ICP27), beta (thymidine kinase and alkaline exonuclease), beta-gamma (glycoprotein D, glycoprotein B, and VP5), and gamma (glycoprotein C) genes, each fused to the chloramphenicol acetyltransferase (CAT) gene. The heterologous target genes consisted of the simian virus 40 early promoter with enhancer and the Rous sarcoma virus long terminal repeat promoter and enhancer each fused to the CAT gene. Target promoter activity was measured by the assay of CAT activity in extracts of transfected cells and by Northern (RNA) blot hybridization of CAT mRNA. The results of these experiments showed that ICP4 activated only HSV-1 target genes, whereas ICP0 activated all of the targets and ICP27 had little effect on any of the targets. ICP4 and ICP0 had a synergistic effect when inducing HSV-1 targets, but they did not have this effect on the heterologous targets pSV2-CAT or pRSV-CAT. In fact, lower levels of CAT activity and CAT mRNA were found in the presence of both effectors than with ICP0 alone. Most interestingly, although the effector plasmid containing the ICP27 gene had little effect on its own, two different and marked effects depending on the target were observed when ICP27 was combined with ICP4 or ICP0 or both. A trans-repression of the induction seen with ICP4 and ICP0 was found when ICP27 was present in the transfections with pSV2-CAT, pRSV-CAT, pICP0-CAT, pICP27-CAT, pTK-CAT, pgD-CAT, pgB-CAT, and pgC-CAT. This resulted in CAT activity levels which were similar to or lower than the basal level of expression of the target genes in the absence of effector plasmids. This trans-repression occurred over a wide range of concentrations of input ICP27 plasmid. In contrast to this repressive effect of ICP27, a trans-activation was seen when ICP4, ICP0, and ICP27 plasmids were combined in transfections with pAE-CAT and pVP5-CAT as targets. This trans-activation also occurred over a 10-fold range of input ICP27 plasmid. These results suggest that ICP27 can facilitate both down

The use of beta-galactosidase as a marker gene to define the regulatory sequences of the herpes simplex virus type 1 glycoprotein C gene in recombinant herpesviruses

The expression of Herpes Simplex Virus 1 (HSV-1) glycoprotein C (gC), a well defined herpesvirus late gene, was studied by linking the promoter-regulatory region of this gene to the coding sequences for the bacterial enzyme, beta-galactosidase (beta-gal). A chimeric gene, containing the beta-gal gene under the control of gC sequences from -1350 to +30 relative to the mRNA start site, was inserted by homologous recombination into the thymidine kinase (TK) locus of the HSV-1 genome. Selection of the TK- recombinant virus by plaque assay was facilitated by addition of a beta-gal indicator to the agarose overlay. Recombinant virus containing the gC promoter-beta-gal chimeric gene faithfully expressed beta-gal as a viral late gene, as shown by the absence of beta-gal expression when viral DNA replication was inhibited with phosphonoacetic acid. In contrast, the inhibition of viral DNA replication had no effect on the expression of beta-gal when the beta-gal gene was under the control of the early HSV-1 TK promoter in a separate recombinant virus. Analysis of recombinant viruses containing 5' to 3' deletions in the gC regulatory region revealed no apparent difference in beta-gal expression as deletions extended from -1350 to -109 base-pairs (bp) before the RNA start site, demonstrating that sequences between -109 and +30 are sufficient for regulated gC expression in the viral genome. Analysis of the mRNA made by these recombinant viruses confirmed the results of the beta-gal assays, and demonstrated that the transcriptional start sites of the gC promoter-beta-gal chimeric genes were the same as the start site of the gC gene.

Gene-specific transactivation by herpes simplex virus type 1 alpha protein ICP27

Herpes simplex virus type 1 (HSV-1) encodes several alpha (immediate-early) gene products that modulate gene expression during viral replication. We report here that the alpha protein ICP27 specifically stimulates expression of a later viral gene, that encoding glycoprotein B (gB). Using temperature-sensitive viral mutants, the effect of ICP27 on HSV-1 protein synthesis was examined at early times after infection or at later times when viral DNA replication was inhibited. Under these conditions, the expression of gB showed a marked dependence on the presence of functional ICP27, whereas several other beta and gamma 1 genes showed a lesser dependence. It was also noted that cells infected with ICP27 temperature sensitive mutants at the nonpermissive temperature showed a reduction in the electrophoretic mobility of the alpha protein ICP4. To examine the mechanism by which ICP27 stimulated gB expression, a plasmid was constructed in which the promoter-regulatory region of the gB gene was fused to the gene encoding chloramphenicol acetyltransferase (CAT). CAT expression from this plasmid was induced significantly by ICP27 expressed from a cotransfected plasmid. Induction of CAT activity by ICP27 correlated well with an increase in the amount of CAT transcripts initiated from the transcriptional start site of the gB gene. The transactivating activity of ICP27 was specific for the gB promoter-regulatory region, as expression from several other HSV-1 promoter-CAT chimeric genes was not stimulated by ICP27. The DNA sequences which conferred the response to ICP27 mapped within 175 base pairs upstream and 41 base pairs downstream of the gB transcriptional start site. Our results suggest that the full expression of gB and perhaps other viral genes during HSV-1 infection requires the combined action of multiple viral transactivators.

DNA sequence and RNA transcription through a site of recombination in a non-neurovirulent herpes simplex virus intertypic recombinant

RE6 is a herpes simplex type-1 (HSV-1) X herpes simplex type-2 (HSV-2) intertypic recombinant that cannot replicate in the adult mouse nervous system. In the accompanying report, we have shown that HSV-1 sequences between 0.698 and 0.721 map units can restore a partial neurovirulent phenotype to RE6. In this report, we have used comparative DNA sequence analysis of RE6, 17syn+ (HSV-1) and HG52 (HSV-2) to demonstrate that this region contains a site of recombination between HSV-1 and HSV-2 sequences in RE6. High resolution transcription analysis has demonstrated that three readily detected transcripts are present in this region of the genome. In addition, the 5' end of a low abundance 5 kb transcript was also located in the right-hand portion of this region. All the transcripts encoded by HSV-1 and HSV-2 in this region of the genome are expressed by the RE6 recombinant. This and our sequence data suggest that the lack of neurovirulence in RE6 is not due to a simple loss in the expression of a transcript or to a defect in a protein encoded by a gene at the site of recombination.

A bi-functional reporter plasmid for the simultaneous transient expression assay of two herpes simplex virus promoters

We have constructed a transient expression vector (pCAL) containing two reporter genes, chloramphenicol acetyltransferase (CAT) and beta-galactosidase (beta-gal) for use in studying herpes simplex virus type 1 (HSV-1) promoter activity in mammalian cells. The construct was designed to be useful in analyzing the simultaneous expression from two different promoters. To test the utility of the vector, we used three HSV-1 promoters that had been characterized previously by workers in this laboratory. Two are early (beta) promoters, for alkaline exonuclease and deoxyuridine triphosphate nucleotidohydrolase; the third promoter controls the major capsid protein transcript and is late (beta gamma). The two different kinetic classes of promoters were ligated in a divergent orientation into pCAL and transfected into rabbit skin fibroblast. Transfected cells were then superinfected with low multiplicities of HSV-1; 18 hr later, we observed the simultaneous expression of both marker genes under control of the respective promoters. The usefulness of such a transient expression reporter vector is discussed.

Dissection of immediate-early gene promoters from herpes simplex virus: sequences that respond to the virus transcriptional activators

The immediate-early promoters of herpes simplex virus give rise to the first series of transcripts after infection. These promoters are composed of compound sequence elements that govern basal level and regulated transcription. The response of three core (truncated) promoters from the herpes simplex virus type 1 IE-4, IE-0, and IE-27 genes to a battery of virus-encoded trans-acting proteins was examined in a short-term transient expression assay system. The results of this study reveal (i) a role for a sequence, 5'---GGGGG---3', flanked by 3 to 5 base pairs of symmetry (the G box), which is present in the upstream region of all immediate-early gene promoters, (ii) a requirement for the consensus sequence protected by ICP4 for autoregulation by this immediate-early gene product, and (iii) an alternative, sequence-independent mechanism for the augmentation of alpha gene expression by the virion-associated transcriptional activator Vmw65, now designated as TIF.

Expression of a cellular gene cloned in herpes simplex virus: rabbit beta-globin is regulated as an early viral gene in infected fibroblasts

We constructed nondefective herpes simplex virus type 1 recombinants bearing the intact rabbit beta-globin gene inserted into the viral gene for thymidine kinase to study the expression of a cellular gene when it is present in the viral genome during lytic viral infections. The globin promoter was activated to high levels during productive infection of Vero cells, giving rise to properly spliced and processed cytoplasmic globin transcripts. Expression of globin RNA occurred with early kinetics, was not affected by blocking viral DNA replication, and was strongly inhibited by preventing viral immediate-early protein synthesis with cycloheximide. These results support the hypothesis that temporal control of herpes simplex virus early gene expression is accomplished by mechanisms that are not restricted to viral promoters. In addition, these data show that a cellular transcript can be correctly processed and can accumulate to high levels during viral infection; this indicates that the mechanisms of virally induced shutoff of host RNA accumulation and degradation of host mRNAs do not depend on sequence-specific differentiation between host and viral RNAs. These findings also suggest that herpesviruses have considerable potential as high-capacity gene transfer vectors for a variety of applications.

Herpes simplex virus virion stimulatory protein mRNA leader contains sequence elements which increase both virus-induced transcription and mRNA stability

To investigate the role of 5' noncoding leader sequence of herpes simplex virus type 1 (HSV-1) mRNA in infected cells, the promoter for the 65,000-dalton virion stimulatory protein (VSP), a beta-gamma polypeptide, was introduced into plasmids bearing the chloramphenicol acetyltransferase (cat) gene together with various lengths of adjacent viral leader sequences. Plasmids containing longer lengths of leader sequence gave rise to significantly higher levels of CAT enzyme in transfected cells superinfected with HSV-1. RNase T2 protection assays of CAT mRNA showed that transcription was initiated from an authentic viral cap site in all VSP-CAT constructs and that CAT mRNA levels corresponded to CAT enzyme levels. Use of cis-linked simian virus 40 enhancer sequences demonstrated that the effect was virus specific. Constructs containing 12 and 48 base pairs of the VSP mRNA leader gave HSV infection-induced CAT activities intermediate between those of the leaderless construct and the VSP-(+77)-CAT construct. Actinomycin D chase experiments demonstrated that the longest leader sequences increased hybrid CAT mRNA stability at least twofold in infected cells. Cotransfection experiments with a cosmid bearing four virus-specified transcription factors (ICP4, ICP0, ICP27, and VSP-65K) showed that sequences from -3 to +77, with respect to the viral mRNA cap site, also contained signals responsive to transcriptional activation.

Transcriptional and post-transcriptional controls establish the cascade of herpes simplex virus protein synthesis

Gene expression by herpes simplex virus type 1 (HSV-1) results in the synthesis of three temporal classes of viral proteins. The three classes of viral proteins are expressed in a cascade manner of sequential dependency. The molecular mechanisms that account for the HSV-1 protein synthesis cascade are poorly understood. In order to provide a detailed description of the metabolic levels at which HSV-1 protein synthesis is regulated, we have measured transcription rates and mRNA accumulation levels for 11 HSV-1 genes. These measurements were made over a time-course of infection in the presence or absence of metabolic inhibitors of either viral protein synthesis or viral DNA synthesis. Our observations show that the protein synthesis cascade of HSV-1 is established as a consequence of mechanisms that regulate both the transcription and accumulation of viral messenger RNA.

Regulation of the herpes simplex virus type 1 late (gamma 2) glycoprotein C gene: sequences between base pairs -34 to +29 control transient expression and responsiveness to transactivation by the products of the immediate early (alpha) 4 and 0 genes

The glycoprotein C (gC) gene of herpes simplex virus type 1 is a true late gene, in that its expression occurs late in infection with a strict requirement for viral DNA replication. Recently, we reported on gC expression during infection with mutant viruses carrying deletions in the gC gene promoter. Analysis of RNA extracted from cells infected with individual mutants showed that the DNA sequences required for regulated expression of this late gene lie within bases -34 to +124 relative to the 5' end of the mRNA. In the present study, the deleted gC promoter sequences were fused to the bacterial chlorampheniol acetyltransferase (CAT) gene and expression was measured in short-term transfection assays after transactivation by infection with HSV or cotransfection with a second plasmid carrying the immediate early genes of HSV-1. The 63 base pair sequence located between -34 to +29 on the gC promoter was sufficient to give induction of CAT activity following infection and on cotransfection with plasmids which code for the immediate early gene products ICP4 and ICPO. This 63 base pair region contains the TATA homology and the transcriptional start site of the gC gene, and apparently contains specific promoter elements not found in a similar region of the HSV TK promoter. This was shown by removing the distal upstream region of the TK promoter, 5' to -37, and found that the TK gene was no longer activated by infection or cotransfection with an alpha 4-alpha 0 gene containing plasmid.

The effect of elevated levels of herpes simplex virus alpha-gene products on the expression of model early and late genes in vivo

The rate of synthesis in vivo and the steady-state level of mRNA of four "model" herpes simplex virus type 1 (HSV-1) genes were measured as a function of high levels of alpha-gene products. The genes studied were ICP4 (alpha), deoxy-UTPase (beta), VP5 (beta gamma), and glycoprotein C (gC, gamma). Accumulation of high levels of alpha proteins was accomplished either by infection with an HSV-1 mutant, temperature-sensitive in ICP4 (ts606) at the nonpermissive temperature then shift-down to permissive temperature, or by infection with wild-type virus under cycloheximide blockage of protein synthesis followed by release. Compared to RNA expression in normal infections, beta gamma and gamma transcription rates were both transiently stimulated under the experimental conditions employed. The greatest effect was seen with the gamma-gC mRNA transcription rates. In addition, at nonpermissive temperatures with ts 606, the amount of expression of gC mRNA was significantly increased over normal early levels, in contrast to the case with the VP5 transcript. The impact of such results on models of HSV gene expression in vivo are discussed.

Transcriptional control signals of a herpes simplex virus type 1 late (gamma 2) gene lie within bases -34 to +124 relative to the 5' terminus of the mRNA

The cis-acting DNA sequences required for regulated expression of a herpes simplex virus type 1 (HSV-1) late (gamma 2) gene were studied by using viruses containing specific deletions in the 5' transcribed noncoding and upstream regions of the HSV-1 glycoprotein C (gC) gene, a model gamma 2 gene. Nine mutant viruses which had variable 5' and 3' deletions within bases -569 to +124 relative to the 5' terminus of the gC mRNA were isolated. The mutants were isolated by a simple in situ hybridization screening procedure not requiring any prior selective pressure for or against expression of the gC gene. Analysis of RNA extracted from cells infected with individual mutants showed that the DNA sequences required for regulated expression of this gamma 2 gene lay within bases -34 to +124. This 158-base-pair fragment was sufficient to confer accurate and quantitative expression of gC mRNA and to maintain the stringent requirement on viral DNA replication for expression of this gene. Moreover, it was found that sequences located between -34 and +14 contained signals essential for expression of gC. To determine whether the -34 to +124 sequences would function as a gamma 2 promoter when moved to another region of the HSV-1 genome, the 158-base-pair fragment was substituted for the normal thymidine kinase promoter-regulatory sequences in the thymidine-kinase gene locus. Transcription of this chimeric gene was regulated as a gamma 2 gene in that its expression in infected cells was dependent on viral DNA synthesis. The only recognizable consensus sequence upstream of the transcription initiation site for this gene was the TATAAA sequence at -30.

Transcriptional control of the mouse prealbumin (transthyretin) gene: both promoter sequences and a distinct enhancer are cell specific

The mouse genomic clone for the prealbumin (transthyretin) gene was cloned, and its upstream regulatory regions were analyzed. The 200 nucleotides 5' to the cap site when placed within a recombinant plasmid were sufficient to direct transient expression in HepG2 (human hepatoma) cells, but this DNA region did not support expression in HeLa cells. The sequence of the 200-nucleotide region is highly conserved between mouse and human DNA and can be considered a cell-specific promoter. Deletions of this promoter region identified a crucial element for cell-specific expression between 151 and 110 nucleotides 5' to the RNA start site. A region situated at about 1.6 to 2.15 kilobases upstream of the RNA start site was found to stimulate expression 10-fold in HepG2 cells but not in HeLa cells. This far upstream element was invertible and increased expression from the beta-globin promoter in HepG2 cells. Unlike the simian virus 40 enhancer, the prealbumin enhancer would not stimulate beta-globin synthesis in HeLa cells, and even the simian virus 40 enhancer did not stimulate the prealbumin promoter in HeLa cells. Thus, we identified in the prealbumin gene two DNA elements that respond in a cell-specific manner: a proximal promoter including a crucial sequence between -108 and -151 nucleotides and a distant enhancer element located between 1.6 and 2.15 kilobases upstream.

Regulation of transcription in vitro from herpes simplex virus genes

In vitro transcription assays were carried out by using as templates DNAs cut from the herpes simplex virus early glycoprotein D gene, the late glycoprotein C gene, the late VP5 gene, and the immediate-early ICP22 gene. Nuclear extracts from suspension cultures of uninfected HeLa cells effectively synthesized RNAs from genes of the immediate-early and delayed-early classes. To a lesser extent, the extracts also used DNAs cut from the late genes as templates. Transcription from the immediate-early gene was inhibited in extracts prepared from infected cells. Analysis of the proteins in infected-cell extracts by gel electrophoresis, transfer to nitrocellulose, and probing with specific antibody demonstrated the presence of the viral regulatory protein ICP4. Chromatographic fractionation of nuclear extract from infected cells yielded a mixture of proteins (fraction VIII) enriched in ICP4 (S.W. Faber and K.W. Wilcox, Nucleic Acids Res., 14:6067-6083, 1986). Addition of fraction VIII to the in vitro assay affected transcription. Depending on the DNA in the assay, an inhibitory or stimulatory effect was observed. Inhibition of RNA synthesis was found when DNA from the immediate-early gene was used as a template, and stimulation was found when DNA from the early or late gene was used.

Transcriptional control of the mouse prealbumin (transthyretin) gene: both promoter sequences and a distinct enhancer are cell specific

The mouse genomic clone for the prealbumin (transthyretin) gene was cloned, and its upstream regulatory regions were analyzed. The 200 nucleotides 5' to the cap site when placed within a recombinant plasmid were sufficient to direct transient expression in HepG2 (human hepatoma) cells, but this DNA region did not support expression in HeLa cells. The sequence of the 200-nucleotide region is highly conserved between mouse and human DNA and can be considered a cell-specific promoter. Deletions of this promoter region identified a crucial element for cell-specific expression between 151 and 110 nucleotides 5' to the RNA start site. A region situated at about 1.6 to 2.15 kilobases upstream of the RNA start site was found to stimulate expression 10-fold in HepG2 cells but not in HeLa cells. This far upstream element was invertible and increased expression from the beta-globin promoter in HepG2 cells. Unlike the simian virus 40 enhancer, the prealbumin enhancer would not stimulate beta-globin synthesis in HeLa cells, and even the simian virus 40 enhancer did not stimulate the prealbumin promoter in HeLa cells. Thus, we identified in the prealbumin gene two DNA elements that respond in a cell-specific manner: a proximal promoter including a crucial sequence between -108 and -151 nucleotides and a distant enhancer element located between 1.6 and 2.15 kilobases upstream.

The control of herpes simplex virus type-1 late gene transcription: a 'TATA-box'/cap site region is sufficient for fully efficient regulated activity

The transcriptional programme of herpes simplex virus type 1 (HSV-1) is organised into three principle phases; immediate-early (IE), early (E) and late. The appearance of IE gene products provides the switch for E transcription. Abundant expression of late genes requires viral DNA replication. There is some overlap between E and late genes according to their degree of dependence on DNA replication. The pattern of expression of gene US11 is regulated with 'true-late' kinetics (Johnson et al., 1986). In a transient assay system, regulation of a plasmid-borne US11 promoter mimics its viral counterpart, and has a similar dependence on DNA replication for abundant expression. Using plasmids which contain a functional HSV-1 origin of replication (ORIS), we have identified the sequence requirements for the expression of late genes. All DNA sequence elements necessary for fully efficient regulated expression of US11 lie within 31 bp of the RNA cap sites; therefore it appears that a late gene promoter consists only of a proximal 'TATA-box' and cap-site region. We tested this hypothesis by removing the distal upstream region of the gD promoter (which is required for its normal regulation as an early promoter) and linking this truncated promoter to ORIS. This resulted in the conversion of gD promoter regulation to late gene kinetics during virus superinfection. The implications of these results for the mechanisms of HSV gene regulation are discussed.

A single regulatory region modulates both cis activation and trans activation of the herpes simplex virus VP5 promoter in transient-expression assays in vivo

A detailed analysis of the expression of the bacterial chloramphenicol acetyltransferase gene controlled by the herpes simplex virus major capsid protein (VP5) promoter showed that this promoter can be functionally separated into an 80-base core region, which has the minimal information required to serve as a pol II promoter but which is not fully activated by viral superinfection or by cotransfections with plasmids bearing functional alpha (immediate-early) genes, and an approximately 100-base regulatory region upstream of the core, which allowed full induction of VP5 promoter-driven chloramphenicol acetyltransferase activity but which repressed the ability of the VP5 core promoter to be cis activated by the simian virus 40 enhancer. This was in distinct contrast to the situation with the alkaline exonuclease promoter (a model early promoter) and defined the regions of this promoter which can be used to study the interaction between viral promoters and putative regulatory proteins induced by viral infection.

Transcriptional control signals of a herpes simplex virus type 1 late (gamma 2) gene lie within bases -34 to +124 relative to the 5' terminus of the mRNA

The cis-acting DNA sequences required for regulated expression of a herpes simplex virus type 1 (HSV-1) late (gamma 2) gene were studied by using viruses containing specific deletions in the 5' transcribed noncoding and upstream regions of the HSV-1 glycoprotein C (gC) gene, a model gamma 2 gene. Nine mutant viruses which had variable 5' and 3' deletions within bases -569 to +124 relative to the 5' terminus of the gC mRNA were isolated. The mutants were isolated by a simple in situ hybridization screening procedure not requiring any prior selective pressure for or against expression of the gC gene. Analysis of RNA extracted from cells infected with individual mutants showed that the DNA sequences required for regulated expression of this gamma 2 gene lay within bases -34 to +124. This 158-base-pair fragment was sufficient to confer accurate and quantitative expression of gC mRNA and to maintain the stringent requirement on viral DNA replication for expression of this gene. Moreover, it was found that sequences located between -34 and +14 contained signals essential for expression of gC. To determine whether the -34 to +124 sequences would function as a gamma 2 promoter when moved to another region of the HSV-1 genome, the 158-base-pair fragment was substituted for the normal thymidine kinase promoter-regulatory sequences in the thymidine-kinase gene locus. Transcription of this chimeric gene was regulated as a gamma 2 gene in that its expression in infected cells was dependent on viral DNA synthesis. The only recognizable consensus sequence upstream of the transcription initiation site for this gene was the TATAAA sequence at -30.

Characterization of the genes encoding herpes simplex virus type 1 and type 2 alkaline exonucleases and overlapping proteins

A detailed sequence analysis of the herpes simplex virus type 1 (HSV-1) and HSV-2 DNA encoding the alkaline exonuclease mRNA clusters has been completed. Three partially colinear mRNAs (2.3, 1.9, and 0.9 kilobases) are completely encoded within the DNA sequence presented. The putative promoter regions of the transcripts were inserted upstream of a plasmid-borne chloramphenicol acetyl transferase (CAT) gene and assayed for their ability to induce transcription of the CAT gene upon low multiplicity of infection with HSV in transient expression assays. We conclude that the expression of all three transcripts appear to be controlled by individual promoters. The 2.3-kilobase mRNA contains an open translational reading frame sufficient to encode 626 amino acids for the HSV-1 alkaline exonuclease enzyme; this value is 620 amino acids for HSV-2. A comparison of the predicted amino acid sequences of the HSV-1 and HSV-2 alkaline exonuclease enzymes revealed significant amino acid differences in the N-terminal portions of the two proteins; however, computer analyses suggest that the three-dimensional structures of the HSV-1 and HSV-2 nuclease enzymes are very similar. The 0.9-kilobase mRNA contains an open reading frame which shares a small amount of out-of-phase overlap with the C-terminal portion of the alkaline nuclease open reading frame. This open reading frame has the capacity to encode a 96-amino-acid polypeptide (10,500 daltons).