The genome of herpesvirus of turkeys: comparative analysis with Marek's disease viruses

The complete coding sequence of the herpesvirus of turkeys (HVT) unique lon g (U-L) region along with the internal repeat regions has been determined. This allows completion of the HVT nucleotide sequence by linkage to the seq uence of the unique short (U-S) region. The genome is approximately 160 kbp and shows extensive similarity in organization to the genomes of Marek's d isease virus serotypes 1 and 2 (MDV-1, MDV-2) and other alphaherpesviruses, The HVT genome contains 75 ORFs, with three ORFs present in two copies. Si xty-seven ORFs were identified readily as homologues of other alphaherpesvi rus genes. Seven of the remaining eight ORFs are homologous to genes in MDV , but are absent from other herpesviruses, These include a gene with simila rity to cellular lipases, The final, HVT-unique gene is a virus homologue o f the cellular NR-13 gene, the product of wh ich belongs to the Eel family of proteins that regulate apoptosis, No other herpesvirus sequenced to date contains a homologue of this gene. Of potential significance is the absenc e of a complete block of genes within the HVT internal repeat that is prese nt in MDV-1. These include the pp38 and meg genes, which have been implicat ed in MDV-1-induced T-cell lymphoma. By implication, other genes present in this region of MDV-1, but missing in HVT, may play important roles in the different biological properties of the viruses.