The dynamic herpesvirus DNA genome: The case of MDV-1 and HSV-1

Herpesviruses evolved from an ancestral viral genome that contained five bl ocks of genes which provide the members of this family of viruses with stru ctural and enzymatic properties. These genes allow the herpesviruses to inf ect a host by entering into the nuclei of the cells, the site of replicatio n and transcription of the viral DNA. The viral mRNAs are released into the cell cytoplasm where synthesis of enzymatic and structural proteins occurs . The latter proteins are responsible for the formation of the infectious v irions. Herpesviruses that were able to adapt to different hosts during the evolution of the species (speciation) had acquired additional genes from t ransposons or retrotransposons that allowed them to successfully maintain t heir hold in the specific vertebrate host. The present overview deals with molecular differences between Marek's disease virus type 1 (MDV-1) and herp es simplex virus type 1 (HSV-1) and the specialized genes that differentiat e MDV- 1 from HSV-1, the promoters of the viral genes that control gene exp ression and the nuclear localization signals. Dynamic changes in the viral genomes that may occur during viral DNA replication and recombination and t heir effects on virus pathogenicity and genome evolution will be discussed.