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

Herpes simplex virus 1 late gene expression is preferentially inhibited during infection of the TAF250 mutant ts13 cell line

A key component of the polymerase II transcription machinery is the transcription factor TFIID, a complex that contains the TATA-box binding protein and several (10-12) associated factors designated as TAFs (TBP-associated factors). ts13 cells, which contain a temperature-sensitive mutant in TAF250, the largest subunit of TFIID, exhibit promoter-specific defects in gene expression at the nonpermissive temperature, suggesting that individual TAFs are required for transcription of specific subsets of eukaryotic genes. Herpes simplex virus 1 (HSV-1) does not replicate in ts13 cells at the nonpermissive temperature, but the point at which the replicative process is blocked is not known. We used the TAF250 defect in ts13 cells to investigate the role of TAF250 in the expression of HSV-1 genes of each temporal class. At a low m.o.i., expression of most immediate-early mRNAs is reduced at the nonpermissive temperature, and consequently, there is little expression of early genes and no viral DNA replication. In contrast, at high m.o.i., expression of immediate-early genes is unaffected by the TAF250 defect and is not dependent on de novo viral protein synthesis. Early genes and early proteins are produced under these conditions, and viral DNA replication ensues, albeit at somewhat reduced levels. In contrast, late gene expression and late protein synthesis are severely restricted, even in the presence of appreciable viral DNA replication. Thus the lack of late protein synthesis is responsible for the inability of HSV-1 to replicate in ts13 cells at the nonpermissive temperature. Further, it appears that late viral gene expression may be preferentially inhibited by the TAF250 mutation in ts13 cells.

Characterization of the initiator and downstream promoter elements of herpes simplex virus 1 late genes

Previously identified cis-acting regulatory elements of herpes simplex virus (HSV) 1 late promoters include a TATA element upstream from the start of transcription, an initiator-like element at the start of transcription, and sequences downstream from the start of transcription. To determine whether these elements are functionally equivalent to similar elements from other eukaryotic genes, model late promoters were constructed using well-characterized regulatory elements from non-HSV genes. These modular promoters were then inserted into the viral genome upstream from a lacZ marker gene. Results showed that a eukaryotic initiator element, along with a TATA element, can function as a late HSV promoter. Several initiator sequences from both viral and nonviral genes were functionally similar to the initiator-like element in HSV-1 late promoters; however, a random sequence of the same size and a similarly located sequence from the HSV-1 early thymidine kinase promoter could not substitute for the initiator element. These results indicate that eukaryotic initiator elements are functionally equivalent to HSV-1 late promoter initiator elements. In addition, the downstream element of the late glycoprotein C promoter was further analyzed by construction of a series of small deletions and insertions. The presence of the downstream glycoprotein C region in a promoter consisting of a strong TATA and initiator element increased mRNA expression by a modest amount; this effect appeared to be sequence specific and dependent on its exact alignment with the upstream elements of the promoter.

Expression of the human immunodeficiency virus gag gene products by a replication-incompetent herpes simplex virus vector

A recombinant replication-incompetent herpes simplex virus vector (vd120/Gag) that expressed the human immunodeficiency virus 1 gag gene and part of the pol gene that encodes the HIV-1 protease was constructed. Examination of cells infected with vd120/Gag revealed the presence of the Gag polyprotein Pr55gag by 12 h post-infection, as well as abundant levels of the proteolytically processed 24-kDa capsid protein. Analysis of vector-infected cells and culture supernatant indicated that the majority of the 24-kDa protein remained cell-associated. Although the HIV-1 Gag polyprotein was produced in vd120/Gag-infected cells, there was no evidence of HIV virus-like particle production upon examination of vector-infected cells by transmission electron microscopy.

Construction and characterization of vaccinia direct ligation vectors

Poxvirus vectors are extensively used as expression vehicles for protein and antigen expression in eukaryotic cells. Customarily, the foreign DNA is introduced into the poxvirus genome by homologous recombination. An alternative method using direct ligation vectors has been used to efficiently construct chimeric genomes in situations not readily amenable for homologous recombination. We describe the construction and characterization of a new set of direct ligation vectors designed to be universally applicable for the generation of chimeric vaccinia genomes. These vectors contain the pair of unique restriction sites NotI and ApaI to eliminate religation of poxvirus arms and fix the orientation of the insert DNA behind strongly expressing constitutive vaccinia promoters. The insertion cassette has been placed at the beginning of the thymidine kinase gene in vaccinia to use drug selection in the isolation of recombinants. These viruses provide a set of universally applicable direct ligation poxvirus cloning vectors, extending the utility of poxvirus vectors for construction and expression of complex libraries.

Herpes simplex type 1:lacZ recombinant viruses. I. Characterization and application to defining the mechanisms of action of known antiherpes agents

Recombinant viruses with the lacZ gene placed under the control of the HSV-1 ICP4, TK and gD regulatory regions were constructed by recombination into the TK locus of HSV-1. Difficulty in isolating ICP4 and gD recombinant viruses with high level, regulated expression of beta-galactosidase was overcome by the use of HSV-1 translational initiation sequences of these genes in place of vector-derived sequences. beta-Galactosidase expression displayed the kinetics particular to each viral class. The maximal expression of beta-galactosidase from the recombinant viruses within a 22-h period (m.o.i. 5) (relative to the ICP4 virus) was gD(3) > gC(2) > ICP4(1) > TK(0.5). The ICP4 virus produces easily quantifiable levels of beta-galactosidase activity for multiplicities of infection from 5 x 10(-4) through 5 over 48 h postinfection. At multiplicities of infection between 2 and 5, ICP4-driven activity was measurable within 2 h postinfection from a monolayer of 3 x 10(4) Vero cells in microtiter wells. Mechanisms of inhibition of several antivirals were probed by using the regulated expression of beta-galactosidase from the ICP4 virus as a marker for viral growth. An experimental antiviral (E3925, IC50 1 microgram/ml) and a neutralizing gD MAb (DUP55306, IC50 0.6 microgram/ml) acted prior to immediate early synthesis, consistent with inhibition of viral entry or uncoating. IFN-gamma inhibited expression of immediate-early synthesis, while having no effect on viral entry. IC50 values for E3925 obtained using either the ICP4 or gD viruses at m.o.i. 0.005, were in good agreement with those obtained by standard plaque assays, but were determined in only 1 day, using a microtiter plate format. Thus, these reporter viruses are useful tools for defining the mechanisms of action of antiherpes agents, while quantitatively reproducing the results for IC50 determinations from standard plaque assays within 24 h in a microtiter plate format.

Plasmid insertion vectors that facilitate construction of herpes simplex virus gene delivery vectors

Plasmid insertion vectors were designed for the expression of foreign genes in recombinant herpes simplex virus (HSV) vectors. One vector, pGal9, was designed for the insertion of foreign genes with their own promoter; a second vector, pGal10, was designed for the insertion of coding sequences downstream from the HSV immediate-early 110K promoter. The 110K promoter directed efficient expression of foreign genes, particularly in replication-incompetent virus recombinants, as shown by the expression of the lacZ and IFN alpha genes. These vectors should be useful for the characterization of various promoters for gene delivery, and for the efficient expression of foreign genes in a variety of cell types.

Replication-incompetent herpesvirus vector delivery of an interferon alpha gene inhibits human immunodeficiency virus replication in human monocytes

Human monocytes and macrophages are nondividing cells that serve as a major reservoir for human immunodeficiency virus (HIV) at all stages of infection. To investigate viral-mediated gene delivery as a means of inhibiting HIV replication in human monocytes, a replication-incompetent herpes simplex virus vector was developed that expressed human interferon alpha. Monocytes infected with this herpes simplex virus vector and then challenged with HIV showed dramatically reduced cytopathic effects and HIV replication compared to control treated monocytes. Similar effects on HIV replication were observed if monocytes were first infected with HIV and then treated with the recombinant vectors. These results demonstrate that replication-incompetent herpes simplex virus gene delivery of interferon alpha directly to human monocytes can greatly decrease HIV replication and suggest that such a vector might deliver therapeutically important genes directly to sites of HIV infection.

Analysis of the gB promoter of herpes simplex virus type 1: high-level expression requires both an 89-base-pair promoter fragment and a nontranslated leader sequence

To investigate the cis-acting sequences involved in regulation of a herpes simplex virus gamma 1 gene, deletion analyses of the glycoprotein B (gB) gene promoter were performed. In transfection assays with gB-chloramphenicol acetyltransferase plasmids, high-level constitutive expression from the gB promoter was found with an 89-bp sequence (-69 to +20). Additional sequences in the 5'-transcribed noncoding leader region (+20 to +136) were required for full stimulation by herpes simplex virus infection. Plasmids with progressive deletions of the gB leader sequence demonstrated that chloramphenicol acetyltransferase expression in infected cells was proportional to the length of the leader region retained. In recombinant viruses containing a gB-gC gene fusion, a similar 83-bp (-60 to +23) region of the gB gene was found to promote accurately initiated gC mRNA from the viral genome with the same kinetics as the wild-type gB gene. Although the kinetics of expression remained the same, RNA abundance was greater with a 298-bp (-260 to +38) promoter than with the 83-bp promoter.

Mutational analysis of two herpes simplex virus type 1 late promoters

To investigate the cis-acting sequence elements that are involved in the regulation of herpes simplex virus type 1 late gene expression, linker-scanning mutations were constructed in the promoters of the glycoprotein C and glycoprotein H genes. Each promoter mutation was inserted upstream of the Escherichia coli lacZ gene in a recombinant virus, and the relative activities of beta-galactosidase expressed from individual recombinant viruses were compared. This analysis identified three sequence elements in each promoter: a TATA element, an element that overlapped the start of transcription, and an element downstream from the start of transcription. Primer extension analysis confirmed these results and showed that mutations in either the TATA element or the initiation sequence could eliminate normal transcription initiation. Analysis of expression from hybrid promoters revealed that the TATA and the initiation elements were interchangeable, at least when correctly aligned, and that the initiation element plays a pivotal role in determining the actual site of transcription initiation.

The relative stability of selected herpes simplex virus type 1 mRNAs

The relative stability of herpes simplex virus type 1 mRNAs was investigated by examination of the decay rates of selected viral transcripts. The synthesis of mRNA was inhibited by the addition of dactinomycin to HSV-1 infected cells, and the abundance of individual transcripts was determined at subsequent times by RNA blot hybridization. For two immediate-early mRNAs, those encoding the 110 and 63 kilodalton immediate-early proteins, RNA synthesis was inhibited at 3 h post-infection and mRNA half-lives of 5-7 h were found. Examination at 5 h post-infection of the early mRNA encoding thymidine kinase as well as the late mRNA encoding glycoprotein H revealed half-lives of 8-11 h. In contrast, at 12 h post-infection, the late mRNAs encoding the glycoproteins C, E, as well as H were found to have half-lives of 14-29 h. These findings suggest that the relative stability of viral mRNA increases late in infection and is dependent upon the time after infection rather than being strictly a property of the mRNA itself.

Upstream promoter elements of the herpes simplex virus type 1 glycoprotein H gene

To investigate the cis-acting sequence elements that are involved in the regulation of herpes simplex virus type 1 late-gene expression, recombinant viruses were constructed that express the Escherichia coli lacZ gene from the promoter of the glycoprotein H (gH) gene. Deletion experiments established an upstream boundary for the gH promoter of no more than 83 bp from the start of gH transcription and showed that the promoter sequences did not overlap with coding sequences of the upstream thymidine kinase (tk) gene. Sequences of the tk gene previously shown to be required for efficient processing of the tk transcript were essential for expression form the gH promoter and included a TATA-like element. In addition, the gH TATA element was specifically mutagenized to substitute the TATA elements of immediate-early, early, and other late viral promoters for the gH TATA element. The results indicated that the TATA element was an interchangeable component of herpes simplex virus type 1 promoters and did not regulate temporal expression.

An insertion vector for the analysis of gene expression during herpes simplex virus infection

A herpes simplex virus type 1 (HSV-1) insertion vector, pGal8, was designed for analysis of herpesvirus promoters during virus infection. This vector contains a multiple cloning site (MCS) positioned at the 5' end of the lacZ gene for the insertion of promoter sequences. The MCS and lacZ are flanked by sequences from the HSV-1 thymidine kinase encoding gene (tk) to direct homologous recombination into the tk locus of the viral genome. The utility of this vector is demonstrated by construction and comparison of recombinant viruses that express lacZ from the promoters of the genes encoding glycoprotein C, glycoprotein H and glycoprotein E.

Expression of the herpes simplex virus type 1 glycoprotein C gene requires sequences in the 5' noncoding region of the gene

The role of the 5' noncoding region of the herpes simplex virus type 1 glycoprotein C (gC) gene in viral gene expression was investigated with recombinant herpesviruses that contained the bacterial beta-galactosidase gene under the control of the gC promoter-regulatory region. Each of these viruses had the same DNA sequences from the start of gC transcription upstream to -114 but had variable segments of the downstream 140-base-pair sequence that is between the start of gC transcription and translation. Analysis of beta-galactosidase expression and mRNA synthesis from these viruses demonstrated the importance of DNA sequences from the start of gC transcription downstream to +38 for optimal expression from the gC promoter.