Sequence of the canine herpesvirus thymidine kinase gene: taxon-preferred amino acid residues in the alphaherpesviral thymidine kinases

Genome Sequence of Canine Herpesvirus

Canine herpesvirus is a widespread alphaherpesvirus that causes a fatal haemorrhagic disease of neonatal puppies. We have used high-throughput methods to determine the genome sequences of three viral strains (0194, V777 and V1154) isolated in the United Kingdom between 1985 and 2000. The sequences are very closely related to each other. The canine herpesvirus genome is estimated to be 125 kbp in size and consists of a unique long sequence (97.5 kbp) and a unique short sequence (7.7 kbp) that are each flanked by terminal and internal inverted repeats (38 bp and 10.0 kbp, respectively). The overall nucleotide composition is 31.6% G+C, which is the lowest among the completely sequenced alphaherpesviruses. The genome contains 76 open reading frames predicted to encode functional proteins, all of which have counterparts in other alphaherpesviruses. The availability of the sequences will facilitate future research on the diagnosis and treatment of canine herpesvirus-associated disease.

Substrate specificity of three viral thymidine kinases (TK): vaccinia virus TK, feline herpesvirus TK, and canine herpesvirus TK

In search of novel suicide gene candidates we have cloned and characterized thymidine kinases from three viruses; vaccinia virus TK (VVTK), feline herpesvirus TK (FHV-TK), and canine herpesvirus TK (CHV-TK). Our studies showed that VVTK primarily is a thymidine kinase, with a substrate specificity mainly restricted to dThd and only minor affinity for dCyd. VVTK also is related closely to mammalian thymidine kinase 1 (TK1), with 66% identity and 75% general homology. Although CHV-TK and FHV-TK are sequence related to herpes simplex virus types 1 thymidine kinase (HSV1-TK), with 31% and 35% identity and a general similarity of 54%, the substrate specificity of these enzymes was restricted to dThd and thymidine analogs.

Nested polymerase chain reaction and in situ hybridization for diagnosis of canine herpesvirus infection in puppies

The usefulness of two nucleic acid detection systems in suspected cases of spontaneous canine herpesvirus (CHV) infection in puppies was evaluated. Formalin-fixed, paraffin-embedded tissues from seven 1-3-week-old naturally infected puppies with lesions characteristic of CHV infection were investigated in a retrospective study. Nested polymerase chain reaction (PCR) and nonradioactive in situ hybridization (ISH) were used to detect nucleotide sequences of the CHV thymidine kinase (TK) gene. According to the original necropsy reports, CHV was isolated in four of the seven puppies using primary canine lung and/or kidney cells. In all seven puppies, gross and histologic lesions consisted of disseminated focal necroses and hemorrhages predominantly in kidneys, lung, liver, and spleen. In addition, few small amphophilic intranuclear inclusion bodies were detected by light microscopy mainly in epithelial cells of kidney, lung, and liver. ISH was performed with a 111-base-pair (bp) digoxigenin-labeled double-stranded DNA probe. Viral DNA was detected in the nuclei of cells near and within lesions. Various cell types, including bronchiolar and alveolar epithelial cells, hepatocytes, renal tubular epithelial cells, neurons, fibrocytes, cardiac myocytes, and endothelial cells, were positive for viral DNA. PCR amplification products of the expected length of 168 bp containing the expected cleavage site for the restriction enzyme EcoRI, derived from paraffin blocks containing lung, kidney, and liver tissues, were detected in all seven puppies. The specificity of the obtained amplicon was further confirmed by Southern blot analysis. ISH and PCR are both useful methods for diagnosing CHV infection in formalin-fixed, paraffin-embedded tissues and are highly specific and sensitive methods for further investigations of the pathogenesis of CHV-induced lesions.

Genomic organization of the canine herpesvirus US region

Canine herpesvirus (CHV) is an alpha-herpesvirus of limited pathogenicity in healthy adult dogs and infectivity of the virus appears to be largely limited to cells of canine origin. CHV's low virulence and species specificity make it an attractive candidate for a recombinant vaccine vector to protect dogs against a variety of pathogens. As part of the analysis of the CHV genome, the authors determined the complete nucleotide sequence of the CHV US region as well as portions of the flanking inverted repeats. Seven full open reading frames (ORFs) encoding proteins larger than 100 amino acids were identified within, or partially within the CHV US: cUS2, cUS3, cUS4, cUS6, cUS7, cUS8 and cUS9; which are homologs of the herpes simplex virus type-1 US2; protein kinase; gG, gD, gI, gE; and US9 genes, respectively. An eighth ORF was identified in the inverted repeat region, cIR6, a homolog of the equine herpesvirus type-1 IR6 gene. The authors identified and mapped most of the major transcripts for the predicted CHV US ORFs by Northern analysis.