| Retroviruses and herpesviruses are common viral pathogens in humans and animals which often co-replicate in the nucleus of infected cells. In this paper, we demonstrate insertion of a nonacute retrovirus, reticuloendotheliosis virus (REV) into a herpesvirus, Marek's disease virus (MDV). REV insertion into MDV occurred during both long-term cocultivation and short-term coinfection. In both experiments, insertions are clustered at the junctions of the short unique region with its inverted repeats. MDV viral clones with REV inserts have been obtained which are able to grow in culture and in chickens. We also provide evidence that REV has inserted into pathogenic strains of MDV in the past. Sequences homologous to REV LTR are found in oncogenic MDV but not in nononcogenic strains. These results raise the possibility that retroviral information may be transmitted by herpesvirus and that herpesvirus expression can be modulated by retroviral elements. In addition, retrovirus may provide a useful tool to characterize herpesviral function by insertional mutagenesis. |
