Prevalence and clinical relevance of thyroid stimulating hormone receptor-blocking antibodies in autoimmune thyroid disease

The prevalence and clinical relevance of thyroid stimulating hormone (TSH) receptor (TSHR) blocking antibodies (TBAb) in patients with autoimmune thyroid disease (AITD) was investigated. Serum TBAb were measured with a reporter gene bioassay using Chinese hamster ovary cells. Blocking activity was defined as percentage inhibition of luciferase expression relative to induction with bovine TSH alone (cut-off 40% inhibition). All samples were measured for TSHR stimulatory antibody (TSAb) and TSHR binding inhibiting immunoglobulins (TBII). A total of 1079 unselected, consecutive patients with AITD and 302 healthy controls were included. All unselected controls were negative for TBAb and TSAb. In contrast, the prevalence of TBAb-positive patients with Hashimoto's thyroiditis and Graves' disease was 67 of 722 (9·3%) and 15 of 357 (4·2%). Of the 82 TBAb-positive patients, thirty-nine (48%), 33 (40%) and 10 (12%) were hypothyroid, euthyroid and hyperthyroid, respectively. Ten patients were both TBAb- and TSAb-positive (four hypothyroid, two euthyroid and four hyperthyroid). Thyroid-associated orbitopathy was present in four of 82 (4·9%) TBAb-positive patients, with dual TSHR antibody positivity being observed in three. TBAb correlated positively with TBII (r = 0·67, P < 0·001) and negatively with TSAb (r = -0·86, P < 0·05). The percentage of TBII-positive patients was higher the higher the level of inhibition in the TBAb assay. Of the TBAb-positive samples with  > 70% inhibition, 87% were TBII-positive. Functional TSHR antibodies impact thyroid status. TBAb determination is helpful in the evaluation and management of patients with AITD. The TBAb assay is a relevant and important tool to identify potentially reversible hypothyroidism.

A novel bioassay for anti-thyrotrophin receptor autoantibodies detects both thyroid-blocking and stimulating activity

Autoantibodies to the thyrotrophin (TSH) receptor (anti-TSHR) are unique, in that they are involved directly in the pathophysiology of certain autoimmune thyroid diseases (AITD). Thyroid-stimulating antibodies (TSAb) act as agonists that activate the thyroid gland and cause Graves' disease. Other anti-TSHR antibodies block TSH and can cause hypothyroidism. Thyroid-blocking antibodies (TBAb) have not been studied as extensively as TSAb. We developed a TBAb bioassay based on a cell line that expresses a chimeric TSHR. The 50% inhibitory concentration of the chimeric Chinese hamster ovary (CHO)-Luc cells was more than five-fold lower compared with the wild-type CHO-Luc cells. We tested the performance of this bioassay using a thyroid-blocking monoclonal antibody K1-70, established an assay cut-off and detected TBAb in 15 of 50 (30%) patients with AITD. Interestingly, the assay detects both TSAb and TBAb and measures the net activity of a mixture of both types of antibodies. There was a high correlation (R(2) 0·9, P < 0·0001) between the results of the TSAb assay and the negative percentage inhibition of the TBAb assay. The TBAb bioassay was approximately 20-fold more sensitive than a commercially available TSHR binding assay (TRAb). In contrast to TRAb, sera with high levels of TBAb activity were able to be diluted several hundred-fold and still exhibit blocking activity above the cut-off level. Thus, this TBAb bioassay provides a useful tool for measuring the activity of anti-TSHR antibodies and may help clinicians to characterize the diverse clinical presentations of patients with AITD.

Novel chimeric thyroid-stimulating hormone-receptor bioassay for thyroid-stimulating immunoglobulins

Thyroid-stimulating immunoglobulins (TSI) are a functional biomarker of Graves' disease (GD). To develop a novel TSI bioassay, a cell line (MC4-CHO-Luc) was bio-engineered to constitutively express a chimeric TSH receptor (TSHR) and constructed with a cyclic adenosine monophosphate (cAMP)-dependent luciferase reporter gene that enables TSI quantification. Data presented as percentage of specimen-to-reference ratio (SRR%) were obtained from 271 patients with various autoimmune and thyroid diseases and 180 controls. Sensitivity of 96% and specificity of 99% for untreated GD were attained by receiver operating characteristic analysis, area under the curve 0·989, 95% confidence interval 0·969-0·999, P = 0·0001. Precision testing of manufactured reagents of high, medium, low and negative SRR% gave a percentage of coefficient-of-variation of 11·5%, 12·8%, 14·5% and 15·7%, respectively. There was no observed interference by haemoglobin, lipids and bilirubin and no non-specific stimulation by various hormones at and above physiological concentrations. TSI levels from GD patients without (SRR% 406 ± 134, mean ± standard deviation) or under anti-thyroid treatment (173 ± 147) were higher (P < 0·0001) compared with TSI levels of patients with Hashimoto's thyroiditis (51 ± 37), autoimmune diseases without GD (24 ± 10), thyroid nodules (30 ± 26) and controls (35 ± 18). The bioassay showed greater sensitivity when compared with anti-TSHR binding assays. In conclusion, the TSI-Mc4 bioassay measures the functional biomarker accurately in GD with a standardized protocol and could improve substantially the diagnosis of autoimmune diseases involving TSHR autoantibodies.

Regulated expression of a Sindbis virus replicon by herpesvirus promoters

We describe the use of herpesvirus promoters to regulate the expression of a Sindbis virus replicon (SINrep/LacZ). We isolated cell lines that contain the cDNA of SINrep/LacZ under the control of a promoter from a herpesvirus early gene which requires regulatory proteins encoded by immediate-early genes for expression. Wild-type Sindbis virus and replicons derived from this virus cause death of most vertebrate cells, but the cells discussed here grew normally and expressed the replicon and beta-galactosidase only after infection with a herpesvirus. Vero cell lines in which the expression of SINrep/LacZ was regulated by the herpes simplex virus type 1 (HSV-1) infected-cell protein 8 promoter were generated. One Vero cell line (V3-45N) contained, in addition to the SINrep/LacZ cDNA, a Sindbis virus-defective helper cDNA which provides the structural proteins for packaging the replicon. Infection of V3-45N cells with HSV-1 resulted in the production of packaged SINrep/LacZ replicons. HSV-1 induction of the Sindbis virus replicon and packaging and spread of the replicon led to enhanced expression of the reporter gene, suggesting that this type of cell could be used to develop sensitive assays to detect herpesviruses. We also isolated a mink lung cell line that was transformed with SINrep/LacZ cDNA under the control of the promoter from the human cytomegalovirus (HCMV) early gene UL45. HCMV carries out an abortive infection in mink lung cells, but it was able to induce the SINrep/LacZ replicon. These results, and those obtained with an HSV-1 mutant, demonstrate that this type of signal amplification system could be valuable for detecting herpesviruses for which a permissive cell culture system is not available.

Detection and quantitation of human respiratory syncytial virus (RSV) using minigenome cDNA and a Sindbis virus replicon: a prototype assay for negative-strand RNA viruses

We describe here a novel approach for detecting and quantitating human respiratory syncytial virus (RSV) based on expression of a reporter gene from an RSV minigenome. BHK cells were cytoplasmically transformed with a noncytopathic Sindbis virus replicon expressing T7 RNA polymerase. These cells were then cotransfected with T7 expression plasmids that contain the cDNA of an RSV minigenome and the genes for RSV nucleocapsid proteins N, P, and L. The minigenome contains a reporter gene such as lacZ or CAT flanked by cis-acting RSV transcription signals. Subsequent infection of these cells with RSV resulted in a high level of reporter gene expression which could be inhibited by ribavirin. Mock-infected cells exhibited background levels of expression. This assay can be used to quantitate RSV and titer neutralizing antibody and may be a valuable tool for screening compounds for anti-RSV activity. It serves as a prototype for other negative-strand RNA viruses.

A rapid assay to screen for drug-resistant herpes simplex virus

A rapid assay was developed to screen for herpes simplex virus (HSV) isolates that are resistant to acyclovir and other antiviral agents. The assay is a modified plaque reduction assay (PRA) in which the number of plaques seen in the absence of acyclovir was compared with that seen in the presence of a single cutoff concentration of acyclovir (2 microg/mL). This assay utilizes a cell line that expresses beta-galactosidase only after infection with HSV. Since histochemically stained plaques are easily visualized, small plaques can be easily enumerated. This allows the assay to be performed on dilutions of untitered specimens in the small wells of a 24-well plate and allows the results to be read only 2 days after inoculation of the virus. The assay performed well compared with a standard PRA and should be a valuable tool in identifying drug-resistant HSV in a timely manner.

Herpes simplex virus gene expression in neurons: viral DNA synthesis is a critical regulatory event in the branch point between the lytic and latent pathways

Herpes simplex virus establishes a latent infection in peripheral neurons. We examined viral gene expression in rat peripheral neurons in vitro and determined that viral gene expression is attenuated and delayed in these neurons compared with that in Vero cells. In addition, using pharmacologic and genetic blocks to viral DNA synthesis, we found that viral alpha and beta gene expression was upregulated by viral DNA synthesis. Although maximal gene expression in neurons requires viral DNA synthetic activity, activation of viral gene expression was seen even in the presence of herpes simplex virus DNA polymerase inhibitors, but not in the absence of the origin-binding protein. Initiation of viral DNA synthesis is apparently a key regulatory event in the balance between the lytic and latent pathways in peripheral neurons.

Transgenic cell lines for detection of animal viruses

Rapid diagnostic assays based on direct detection of viral antigen or nucleic acid are being used with increasing frequency in clinical virology laboratories. Virus culture, however, remains the only way to detect infectious virus and to analyze clinically relevant viral phenotypes, such as drug resistance. Growth of viruses in cell culture is labor intensive and time-consuming and requires the use of many different cell lines. Transgenic technology, together with increasing knowledge of the molecular pathways of virus replication, offers the possibility of using genetically modified cell lines to improve virus growth in cell culture and to facilitate detection of virus-infected cells. Genetically modifying cells so that they express a reporter gene only after infection with a specific virus can allow the detection of infectious virus by rapid and simple enzyme assays such as beta-galactosidase assays without the need for antibodies. Although transgenic cells have recently been successfully used for herpes simplex virus detection, much more work needs to be done to adapt this technology to other human viral pathogens such as cytomegalovirus and respiratory viruses. This review offers some strategies for applying this technology to a wide spectrum of animal viruses.

Varicella-zoster virus gene 51 complements a herpes simplex virus type 1 UL9 null mutant

Varicella-zoster virus (VZV) gene 51 encodes a protein which is homologous to UL9, the origin of DNA replication-binding protein of herpes simplex virus type 1. No genetic information is available on VZV gene 51, but its product has been shown to bind to virtually the same recognition sequence as does UL9 (D. Chen and P. D. Olivo, J. Virol. 68:3841-3849, 1994; N. D. Stow, H. M. Weir, and E. C. Stow, Virology 177:570-577, 1990). We report here that gene 51 can complement a UL9 null mutant (hr94) (A. K. Malik, R. Martinez, L. Muncy, E. P. Carmichael, and S. K. Weller, Virology 190:702-715, 1992), but at a level which is only 20% of that of UL9. Quantitation of viral DNA synthesis suggests that this phenotype is due to a defect in viral DNA synthesis. Regardless, the ability of VZV gene 51 to complement UL9 suggests that alphaherpesviruses have a highly conserved mechanism of initiation of viral DNA synthesis.

Antiviral susceptibility testing with a cell line which expresses beta-galactosidase after infection with herpes simplex virus

Despite increasing concern about drug-resistant herpes simplex virus (HSV), antiviral susceptibility testing is not routinely performed by most clinical virology laboratories. This omission is in large part because the most widely accepted method, the plaque reduction assay (PRA), is cumbersome to perform and results are rarely available in time to influence treatment. We report here the development of a sensitivity test for HSV which utilizes a cell line (VeroICP6LacZ#7) that expresses beta-galactosidase activity after infection with HSV such that infected cells can be detected by histochemical staining. We designed an assay in which 10-fold dilutions of virus stocks with undetermined titers were inoculated onto VeroICP6LacZ#7 cells in a 24-well tissue culture dish. Forty-eight hours after infection, the cell monolayers were histochemically stained. Plaques appear blue against a clear background and are thus easily visualized at 48 h. As with the standard PRA, the 50% inhibitory concentration (IC50) was reported as the concentration of an antiviral drug that reduces the number of plaques by 50%. Evaluation of 10 well-characterized laboratory strains and 12 clinical HSV isolates showed that the IC50 determined by this method correlated in all instances with the IC50 determined by the PRA. This method is easy to use and eliminates the need to determine the titer of the virus, and results are available within 48 h of the detection of the virus. VeroICP6Lac#7 cells are a useful tool for performing HSV antiviral susceptibility testing and could be used in a number of different formats to facilitate the identification of drug-resistant isolates of HSV.

The varicella-zoster virus origin-binding protein can substitute for the herpes simplex virus origin-binding protein in a transient origin-dependent DNA replication assay in insect cells

We isolated two recombinant baculoviruses each of which expresses a varicella-zoster virus (VZV) homolog of one of the seven herpes simplex virus type 1 (HSV-1) genes required for DNA replication. We performed transient origin-dependent DNA replication assays in insect cells in which we substituted a baculovirus which expresses a VZV protein for a baculovirus which expresses its HSV homolog. VZV gene 51 protein was found to be able to support origin-dependent DNA synthesis when it was substituted for UL9, the HSV-1 origin-binding protein (OBP). This occurred whether an HSV-1 or a VZV origin-containing plasmid was used in the assay. These results suggest that VZV gene 51 protein is able to interact with the HSV replication machinery, and in light of the extensive structural divergence of these proteins, it suggests that initiation of VZV and HSV-1 DNA synthesis may involve a limited number of interactions between the OBP and other replication factors. Substitution of infected-cell protein 8 (ICP8), the major single-stranded DNA-binding protein of HSV-1, with VZV gene 29 protein, however, did not result in amplification of plasmids containing either an HSV-1 or a VZV origin. In the absence of ICP8, addition of both VZV gene 51 protein and gene 29 protein was also negative for origin-dependent replication whether or not UL9 was present. Although demonstration that our baculovirus-expressed VZV gene 29 protein is functional for DNA replication will await development of a VZV replication system, our results suggest that VZV gene 29 protein is unable to interact functionally with one or more of the HSV replication proteins. This approach should contribute to efforts to define the interactions among the alphaherpesvirus DNA replication proteins.

Infection of sympathetic and sensory neurones with herpes simplex virus does not elicit a shut-off of cellular protein synthesis: implications for viral latency and herpes vectors

Infection of non-neuronal cell types with herpes simplex virus type 1 (HSV-1) results in the degradation of host mRNA (Kwong & Frenkel 1987) and a shutoff in host protein synthesis (Roizman et al. 1965). This effect is mediated by a virion associated protein that is encoded by the viral vhs gene (Read & Frenkel 1983). This virion host shutoff (VHS) helps regulate viral gene expression and promotes efficient viral replication during the lytic cycle (Kwong & Frenkel 1987). Cultured sympathetic and sensory neurones, in contrast to primary rat fibroblasts, PC-12 cells, and Vero cells, showed no reduction in protein synthesis following infection with HSV-1. The resistance of neurones to VHS may be important in allowing establishment of a latent infection. In addition, this finding has a favourable impact on the idea of using HSV as a vector to deliver foreign genes into neurones.

Expression of the varicella-zoster virus origin-binding protein and analysis of its site-specific DNA-binding properties

The varicella-zoster virus (VZV) genome contains homologs to each of the seven herpes simplex virus (HSV) genes that are required for viral DNA synthesis. VZV gene 51 is homologous to HSV UL9, which encodes an origin of DNA replication binding protein (OBP). It was previously shown, by using a protein A fusion protein, that the product of gene 51 is a site-specific DNA-binding protein which binds to sequences within the VZV origin (Stow et al., Virology 177:570-577, 1990). In this report, gene 51 was expressed in an in vitro translation system. Rabbit antiserum raised against the carboxyl-terminal 20 amino acids was used to confirm expression of the full-length gene 51 protein, and site-specific DNA-binding activity was demonstrated in a gel retardation assay. The origin-binding domain was located within a 263-amino-acid region of the carboxyl terminus by using a series of deletion mutants. The affinity of binding of the VZV OBP to the three binding sites in the VZV origin was found to be similar. In addition, as with UL9, a CGC triplet within a 10-bp consensus sequence is critical to the interaction between the OBP and the origin. The HSV and VZV OBPs, therefore, appear to have virtually identical recognition sequences despite only 33% identity and 44% similarity in the primary structure of their site-specific DNA-binding domains.

Detection of herpes simplex virus by measurement of luciferase activity in an infected-cell lysate

A stably transformed cell line (BHKICP6LucA6) has been isolated which expresses high levels of luciferase activity following infection with herpes simplex virus (HSV). The genome of this cell line contains an HSV-1 promoter-luciferase chimeric gene. Infected BHKICP6LucA6 cells exhibit a level of luciferase activity 5 x 10(5) higher than mock-infected cells. This signal-to-noise ratio is of a sufficient magnitude that measurement of the luciferase activity of an infected-cell lysate can detect a single infected cell when a practical number of cells is used in the assay. This approach to the detection of infectious virus could be useful in a number of circumstances and may be adaptable to an automated assay which could become a useful means for diagnostic laboratories to detect viruses in clinical specimens.

A cell line that expresses a reporter gene in response to infection by Sindbis virus: a prototype for detection of positive strand RNA viruses

We describe a stably transformed cell line (BHKSINLuc2) that contains a defective Sindbis virus genome under the control of a Rous sarcoma virus promoter and the luciferase gene downstream of the viral subgenomic RNA promoter. This cell line expresses high levels of luciferase activity following infection with Sindbis virus and provides a sensitive assay for titering variants of Sindbis virus that lack the structural protein genes, in particular, Sindbis virus replicons that express heterologous proteins. Cell lines such as this may be of value for detection of positive-strand RNA viruses.

A truncated herpes simplex virus origin binding protein which contains the carboxyl terminal origin binding domain binds to the origin of replication but does not alter its conformation

We have studied the DNA binding properties of a polypeptide consisting of the carboxyl terminal 37% of UL9, the herpes simplex virus type 1 (HSV-1) origin of replication binding protein. Using a Sindbis virus expression system, we expressed and partially purified this truncated form of UL9 (UL9CT) which contains the site-specific DNA binding domain. UL9CT specifically recognized UL9 binding sites on a 200 base pair DNA fragment containing the HSV origin ori(s) and appeared to bind as a dimer to each site. DNAse I footprint analysis showed that UL9CT protected the two high affinity binding sites of ori(s), but unlike full-length UL9, UL9CT did not induce a conformational change in the origin. Addition of anti-UL9CT antibody to the UL9CT-origin complex, however, caused a conformational change in the origin to be evident. Our results suggest that a domain, or domains, in the amino terminus are necessary for a UL9-induced origin conformational change to occur and that UL9-UL9 interactions between binding sites are involved.

Evaluation of a genetically engineered cell line and a histochemical beta-galactosidase assay to detect herpes simplex virus in clinical specimens

A novel histochemical method was compared with a cytopathic effect (CPE) assay for the identification of herpes simplex virus (HSV) in clinical specimens. The method utilizes a stably transformed cell line (BHKICP6LacZ-5) that expresses beta-galactosidase only after infection with HSV. A total of 96 specimens submitted to our diagnostic virology laboratory were analyzed. Thirty-one specimens contained HSV as evidenced by positive CPE, and all were positive for beta-galactosidase staining. CPE were not evident for 2 or more days in 15 of the 31 positive specimens, whereas the histochemical stain was positive in all 31 positives by 16 to 24 h. This preliminary study shows that the BHKICP6LacZ-5 cell line can be used in a rapid, sensitive, and specific assay for the detection of HSV in clinical specimens.

Gene delivery to neurons: is herpes simplex virus the right tool for the job?

Herpes simplex virus (HSV)-derived vectors are currently being developed for the introduction of foreign DNA into neurons. HSV vectors can facilitate a range of molecular studies on postmitotic neurons and may ultimately be used for somatic cell gene therapy for certain neurologic diseases. In this article, the salient features of the pathologenesis and molecular biology of HSV relevant to its use as a vector are described, along with an overview of the methods used to derive these vectors. The accomplishments which have been made to date using the HSV vector system are discussed, with emphasis on the issues of this technology which remain to be addressed. HSV has the potential to be a most useful tool for neuronal cell transgenesis and it is likely that important neurobiological questions will be answered using this vector system.

Isolation of a cell line for rapid and sensitive histochemical assay for the detection of herpes simplex virus

A cell line which can be used in a simple, sensitive, and rapid histochemical assay was isolated for detection of herpes simplex virus (HSV). The cell line was derived by selection of G418 resistant colonies following co-transfection of baby hamster kidney cells with a plasmid which contains a G418 antibiotic resistance marker and a plasmid which contains the Escherichia coli LacZ gene placed behind an inducible HSV promoter. The promoter is from HSV-1UL39 which encodes ICP6, the large subunit of ribonucleotide reductase (RR1). This promoter has a number of features which make it ideal for the detection of HSV. First, there is no constitutive expression from this promoter in uninfected cells. Second, activation of the promoter appears to be specific for HSV. Third, expression from this promoter occurs within hours after infection. Fourth, this promoter is strongly transactivated by the virion associated trans-activator protein VP16. As early as six hours after infection HSV-infected cells can be detected by histochemical staining for beta-galactosidase activity. Infected cells stain intensely blue whereas uninfected cells show no staining, and a single infected cell can easily be recognized in a microscopic field of uninfected cells. Both HSV-1 and HSV-2 are detected with this cell line, but after infection with human cytomegalovirus (HCMV), varicella zoster virus (VZV), adenovirus, and sindbis virus no blue cells were detected. Quantitation of HSV-1 stocks on this cell line by counting blue cell forming units (BFU) reveals that the number of BFU/ml closely approximates the number of plaque forming units (PFU)/ml as determined by plaque assays on the parent cell line. This cell line should provide a useful adjunct in the diagnostic virology laboratory for the rapid detection of HSV in clinical specimens.

A gene delivery/recall system for neurons which utilizes ribonucleotide reductase-negative herpes simplex viruses

We present data which show that ribonucleotide (RR)-negative herpes simplex virus type-1 (HSV-1) is a useful vector for gene delivery into neuronal cells. For these studies we used hrR3, a genetically engineered HSV-1 mutant which has an in-frame insertion of the bacterial lacZ gene into the HSV gene that encodes the large subunit (ICP6) of RR. After infection of rat primary sympathetic neuronal cultures with hrR3, the ICP6::lacZ chimeric gene was expressed, as shown by blue staining of the cells upon exposure to X-Gal, a chromogenic beta-galactosidase substrate. When the infection was performed in the presence of acyclovir, hrR3 appeared to become "latent"; neither infectious virus nor beta-galactosidase activity was detectable in these neuronal cultures at 3 weeks after the acyclovir was removed. However, beta-galactosidase activity was inducible in the "latent" cultures by superinfection with ICP6 delta (a RR-negative deletion mutant) without resulting in the "reactivation" of hrR3 and without apparent cytopathic effects. In contrast, superinfection with ICP6 delta + 3.1, a virus derived by marker rescue of ICP6 delta, resulted in the expression of lacZ, the release of hrR3 into the culture medium, and cytopathic effects. The introduction of a foreign gene into neuronal cells by a RR-negative herpes simplex virus, and the subsequent induction of gene expression by another noncomplementing virus, may constitute a prototype gene delivery/recall system for neurons.

Enzymatic activities of overexpressed herpes simplex virus DNA polymerase purified from recombinant baculovirus-infected insect cells

Biochemical characterization of the herpes simplex virus (HSV) DNA polymerase, a model DNA polymerase and an important target for antiviral drugs, has been limited by a lack of pure enzyme in sufficient quantity. To overcome this limitation, the HSV DNA polymerase gene was introduced into the baculovirus, Autographa californica nuclear polyhedrosis virus, under the control of the polyhedrin promoter to give rise to a recombinant baculovirus, BP58. BP58-infected Spodoptera frugiperda insect cells expressed a polypeptide that was indistinguishable from authentic polymerase by several immunological and biochemical properties, at levels approximately ten-fold higher per infected cell than found in HSV-infected Vero cells. The DNA polymerase was purified to apparent homogeneity from BP58-infected insect cells. Using activated DNA as primer-template, the purified enzyme exhibited specific activity similar to that of enzyme isolated from HSV-infected Vero cells, indicating that additional polymerase-associated proteins from HSV-infected cells are not critical for activity with this primer-template. 3'-5' exonuclease activity co-purified with the BP58-expressed HSV DNA polymerase, demonstrating that this activity is intrinsic to the polymerase polypeptide. The purified enzyme also exhibited RNAse H activity. The recombinant baculovirus should permit detailed biochemical and biophysical studies of this enzyme.

Herpes simplex virus 1 helicase-primase: a complex of three herpes-encoded gene products

In an earlier report, we described a DNA helicase that is specifically induced upon infection of Vero cells with herpes simplex virus 1. We have purified this enzyme to near homogeneity and found it to consist of three polypeptides with molecular weights of 120,000, 97,000, and 70,000. Immunochemical analysis has shown these polypeptides to be the products of three of the genes UL52, UL5, and UL8 that are required for replication of a plasmid containing a herpes simplex 1 origin (oriS). In addition to helicase activity, the enzyme contains a tightly associated DNA primase. Thus, the three-subunit enzyme is a helicase-primase complex that may prime lagging-strand synthesis as it unwinds DNA at the viral replication fork.

Herpes simplex virus type 1 gene products required for DNA replication: identification and overexpression

Seven herpes simplex virus (HSV) genes have been shown recently to be necessary and sufficient to support the replication of origin-containing plasmids. Two of these genes (pol and dbp) encode well-known DNA replication proteins (the DNA polymerase and the major single-stranded DNA binding protein), and a third gene (UL42) encodes a previously identified infected-cell protein which binds tightly to double-stranded DNA. The products of the four remaining genes have not previously been identified. Using the predicted amino acid sequence data (D.J. McGeoch, M.A. Dalrymple, A. Dolan, D. McNab, L.J. Perry, P. Taylor, and M.D. Challberg, J. Virol. 62:444-453; D.J. McGeoch and J.P. Quinn, Nucleic Acids Res. 13:8143-8163), we have raised rabbit antisera against the products of all seven genes. We report here the use of these reagents to identify these proteins in infected cells. All seven proteins localized to the nucleus and were expressed in a manner consistent with the idea that they are the products of early genes. Various immunological assays suggest that four of these proteins (UL5, UL8, UL9, and UL52) are made in infected cells in very low abundance relative to the other three. To improve our ability to study these proteins, we have expressed UL5, UL8, UL9, and UL52 in insect cells by using the baculovirus expression system. The HSV protein made in insect cells were immunoprecipitable with the appropriate antisera, and the size of each protein was indistinguishable from the size of the corresponding protein made in HSV-infected Vero cells. Our data offer strong support for the accuracy of open reading frames proposed by McGeoch et al. In addition, the antisera and the overproduced HSV replication proteins should be useful reagents with which to analyze the biochemistry of HSV DNA replication.

Herpes simplex virus DNA replication: the UL9 gene encodes an origin-binding protein

Herpes simplex virus 1 contains seven genes that are necessary and sufficient for origin-dependent DNA synthesis in cultured cells. We have expressed the product of one of these genes, UL9, in insect cells by using a baculovirus expression vector. The apparent size of the UL9 protein, both in insect cells and in herpes simplex virus-infected Vero cells, is 82,000 Da. By using an immunoassay for protein-DNA interaction, we have shown that UL9 protein binds specifically to the herpes simplex virus origins of DNA replication, oriS and oriL. DNase I "footprint" analysis has shown that the UL9 protein interacts with two related sites on oriS, located on each arm of a nearly perfect palindrome. Our data strongly suggest that the origin-binding activity described previously by Elias et al. [Elias, P., O'Donnell, M. E., Mocarski, E. S. & Lehman, I. R. (1986) Proc. Natl. Acad. Sci. USA 83, 6322-6326] is the product of the UL9 gene.

Template-directed arrest of mammalian mitochondrial DNA synthesis

Mammalian mitochondrial DNA often contains a short DNA displacement loop at the heavy-strand origin of replication. This short nascent DNA molecule has been used to study site-specific termination of mitochondrial DNA synthesis in human and mouse cells. We examined D-loop strand termination in two distantly related artiodactyls, the pig and the cow. Porcine mitochondrial DNA was unique among mammals in that it contained only a single species of D-loop single-stranded DNA. Its 3' end mapped to a site 187 nucleotides from the 5' end of the proline tRNA gene. This site was 21 and 47 nucleotides 5' to two very similar sequences (5' ACATATPyATTAT 3') which are closely related to the human and mouse termination-associated sequences noted by Doda et al. (J. N. Doda, D. T. Wright, and D. A. Clayton, Proc. Nat. Acad. Sci. USA 78:616-6120, 1981). Bovine mitochondrial DNA contained three major D-loop DNA species whose 3' ends mapped to three different sites. These sites were not found in the porcine sequence. However, the bovine termination sites were located 60 to 64 base pairs 5' from sequences which were also very similar to the termination-associated sequences present in pigs and other mammals. These results firmly establish the concept that arrest of heavy-strand DNA synthesis is an event determined, at least in part, by template sequence. They also suggest that arrest is determined by sequences which are a considerable physical distance away from the actual termination site.

Heterogeneous mitochondrial DNA D-loop sequences in bovine tissue

Mitochondrial DNA from bovine tissue contains heterogeneous sequences located within an evolutionary conserved cytosine homopolymer sequence near the 5' end of the D-loop region. This part of the mammalian mitochondrial genome is known to contain the origin of heavy strand DNA synthesis and the major transcriptional promoter for each strand. Nucleotide sequence analysis of cloned DNA and electrophoretic analysis of appropriate small fragments from animal tissue reveal a population of length polymorphs containing from nine to 19 cytosine residues. No individual length species represents more than 40% of the population. These data imply a state of significant intraanimal mtDNA sequence heterogeneity, which most likely occurs intracellularly as well. The localization of variability to a homopolymer run suggests that replication slip-page generated the sequence population. We also report that when recombinant clones containing this region are repeatedly passaged in E. coli, they begin to regenerate length variation similar to that seen in animal mtDNA.

Nucleotide sequence evidence for rapid genotypic shifts in the bovine mitochondrial DNA D-loop

Mitochondrial DNA (mtDNA) is unusual in its rapid rate of evolution and high level of intraspecies sequence variation. The latter is thought to be related to the strict maternal inheritance of mtDNA, which effectively isolates within a species mitochondrial gene pools that accumulate mutations and vary independently. A fundamental and as yet unexplained aspect of this process is how, in the face of somatic and germ-line mtDNA ploidy of 10(3) to 10(5) (refs 4, 5), individual variant mtDNA molecules resulting from mutational events can come to dominate the large intracellular mtDNA population so rapidly. To help answer this question, we have determined here the nucleotide sequence of all or part of the D-loop region in 14 maternally related Holstein cows. Four different D-loop sequences can be distinguished in the mtDNA of these animals. One explanation is that multiple mitochondrial genotypes existed in the maternal germ line and that expansion or segregation of one of these genotypes during oogenesis or early development led to the rapid genotypic shifts observed.