Cloning and expression of an equine herpesvirus 1 origin-binding protein

Structural and biophysical characterization of the proteins interacting with the herpes simplex virus 1 origin of replication

The C terminus of the herpes simplex virus type 1 origin-binding protein, UL9ct, interacts directly with the viral single-stranded DNA-binding protein ICP8. We show that a 60-amino acid C-terminal deletion mutant of ICP8 (ICP8DeltaC) also binds very strongly to UL9ct. Using small angle x-ray scattering, the low resolution solution structures of UL9ct alone, in complex with ICP8DeltaC, and in complex with a 15-mer double-stranded DNA containing Box I of the origin of replication are described. Size exclusion chromatography, analytical ultracentrifugation, and electrophoretic mobility shift assays, backed up by isothermal titration calorimetry measurements, are used to show that the stoichiometry of the UL9ct-dsDNA15-mer complex is 2:1 at micromolar protein concentrations. The reaction occurs in two steps with initial binding of UL9ct to DNA (Kd approximately 6 nM) followed by a second binding event (Kd approximately 0.8 nM). It is also shown that the stoichiometry of the ternary UL9ct-ICP8DeltaC-dsDNA15-mer complex is 2:1:1, at the concentrations used in the different assays. Electron microscopy indicates that the complex assembled on the extended origin, oriS, rather than Box I alone, is much larger. The results are consistent with a simple model whereby a conformational switch of the UL9 DNA-binding domain upon binding to Box I allows the recruitment of a UL9-ICP8 complex by interaction between the UL9 DNA-binding domains.

Effective treatment of respiratory alphaherpesvirus infection using RNA interference

BACKGROUND

Equine herpesvirus type 1 (EHV-1), a member of the Alphaherpesvirinae, is spread via nasal secretions and causes respiratory disease, neurological disorders and abortions. The virus is a significant equine pathogen, but current EHV-1 vaccines are only partially protective and effective metaphylactic and therapeutic agents are not available. Small interfering RNAs (siRNA's), delivered intranasally, could prove a valuable alternative for infection control. siRNA's against two essential EHV-1 genes, encoding the viral helicase (Ori) and glycoprotein B, were evaluated for their potential to decrease EHV-1 infection in a mouse model. METHODOLOGY/PRINCIPAL FNDINGS: siRNA therapy in vitro significantly reduced virus production and plaque size. Viral titers were reduced 80-fold with 37.5 pmol of a single siRNA or with as little as 6.25 pmol of each siRNA when used in combination. siRNA therapy in vivo significantly reduced viral replication and clinical signs. Intranasal treatment did not require a transport vehicle and proved effective when given up to 12 h before or after infection.

CONCLUSIONS/SIGNIFICANCE

siRNA treatment has potential for both prevention and early treatment of EHV-1 infections.

Functional characterization of Marek's disease virus (MDV) origin-binding protein (OBP): analysis of its origin-binding properties

In previous studies, we identified a Marek's disease virus (MDV) origin-binding protein (OBP) gene that is highly homologous to the herpes simplex virus type 1 UL9 gene that encodes an OBP and functions as an initiator protein for viral DNA replication. In this study, a protein of 95 kDa was produced in coupled in vitro transcription-translation reaction with the plasmid containing the wild type MDV OBP gene. The in vitro synthesized protein was detected by immunoprecipitation with a penta-histidine specific monoclonal antibody. Further characterization of MDV OBP was accomplished using electrophoretic mobility shift assay (EMSA) with the in vitro expressed MDV OBP using a double-stranded (ds) 26-mer oligonucleotide as the probe, which was designed from the putative MDV OBP binding site present in the serotype 1 or 2 MDV replication origin. The EMSA results indicated that MDV OBP could form a protein-DNA complex with the ds 26-mer oligonucleotide designed from serotype 1 or 2 replication origin. A series of 26-mer oligonucleotides with two-base-pair (bp) substitution across the putative MDV OBP binding site were used in competitive EMSA to determine the recognition sequence for the MDV OBP. The results demonstrated that the recognition sequence for MDV OBP was the TTCGCACC that is a subset of a 9-bp element (CGTTCGCAC) conserved in the replication origins of alphaherpesviruses. Furthermore, the results of EMSA with a series of deletion mutants from the N-terminus of MDV OBP indicated that the origin-binding domain was located at the amino acids region 528 to 841 of the wild-type MDV OBP. Taken together, our results suggest that the MDV OBP gene encodes an OBP of MDV.

Cloning and sequence analysis of a Marek's disease virus origin binding protein (OBP) reveals strict conservation of structural motifs among OBPs of divergent alphaherpesviruses

Marek's disease virus (MDV) is a highly cell-associated avian herpesvirus. In its natural host, MDV induces Marek's disease (MD), a lethal condition characterized by malignant lymphoma of T cells. Although symptoms of MD may be prevented by vaccination, no practical pharmacological method of control has been widely accepted. Viral replication represents a point at which pharmacological control of herpesvirus infection may be most successful. However, this requires detailed knowledge of viral replication proteins. Studies in HSV-1 DNA replication implicate the UL9 protein as a key initiator of replication. For example, binding of UL9 to HSV-1 origins is a prerequisite for assembly of additional replication proteins. In this study, a protein, whose apparent molecular size is similar to that of HSV-1 UL9, was identified in extracts of MDV infected cells by western blot analysis with anti-HSV-1 UL9 antibody. A putative MDV UL9 gene was subsequently identified through sequencing of MDV genome fragments (BamHI G and C). Extended DNA sequence analysis revealed an open reading frame (ORF) which could encode a protein homologous to HSV-1 UL9. The MDV UL9 ORF encodes 841 amino acids, producing a sequence 49% identical to HSV-1 UL9 and 46% identical to VZV gene 51 product (VZV UL9). MDV UL9 shares numerous structural motifs with HSV-1 and VZV UL9 proteins, including six conserved N-terminal helicase motifs, an N-terminal leucine zipper motif, a C-terminal pseudo-leucine zipper sequence, and a putative helix-turn-helix structure.

Human herpesvirus 6B origin-binding protein: DNA-binding domain and consensus binding sequence

We previously demonstrated by a DNA-binding assay that the human herpesvirus 6B (HHV-6B) replication origin has a structure similar to those of alphaherpesviruses, although the HHV-6B and herpes simplex virus type 1 (HSV-1) origin-binding proteins (OBPs) and origins are not interchangeable. Here we describe additional properties of the interaction between HHV-6B OBP and the HHV-6B origin. Competitive electrophoretic mobility shift assays (EMSAs) with DNA duplexes containing single-base alterations allowed deduction of a consensus DNA sequence for HHV-6B-specific OBP binding, YGWYCWCCY, where Y is T or C and W is T or A, while that for HSV-1-specific binding was reported to be YGYTCGCACT. By EMSA, the HHV-6B OBP DNA-binding domain was mapped to a segment containing amino acids 482 to 770. However, in Southwestern (protein-DNA) blotting, the region sufficient for the DNA binding encompassed only amino acids 657 to 770. Similarly, Southwestern blotting showed that amino acids 689 to 851 of HSV-1 OBP had HSV-1 origin-binding activity, although this region was insufficient for origin binding in the EMSA. Although the longer DNA-binding domains identified by EMSA have marginal overall homology among HHV-6B and alphaherpesvirus OBP homologs, the smaller regions sufficient for the binding observed by Southwestern blotting have significant similarity. From these results, we propose a hypothesis that the DNA-binding domain of herpesvirus OBPs consists of two subdomains, one containing a conserved motif that contacts DNA directly, and another, less well conserved, that may modulate either the conformation or accessibility of the binding domain.

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.