Development of the hot spot–combined PCR assay for detection of retroviral insertions into Marek’s disease virus

Abstract

A two-step PCR, the Hot Spot–combined PCR assay, was developed for the identification and characterization of recombinant viruses in Marek’s disease (herpes) and retrovirus co-infections. In the first PCR the herpesvirus genomic fragment, that was recognized in previous studies as a hot spot site for retroviral integration was amplified [reviewed in Bronovskis, P., Kung, H.-J., 1996. Retrotransposition and herpesvirus evolution. Virus Genes 11, 259–270]. The products served for a second amplification step, performed in six PCR sets, using the six possible combinations of the two herpes and the retrovirus primer sets. Development of the assay employed DNA of the recombinant virus, RM1, which was created by in vitro co-cultivation of Marek’s disease and reticuloendotheliosis viruses [Isfort et al., 1992. Proc. Natl. Acad. Sci. 89, 991–995; Witter et al., 1997. Avian Dis. 41, 407–421]. As the retroviral insertion site and junction sequences were determined previously [Jones et al., 1996. J. Virol. 70, 2460–2467], RM1 served in the present study as a test virus for the development of the new assay. It is shown now that the Hot Spot-combined PCR can detect the retroviral insert in RM1, the MDV integration site and the insert orientation. For confirmation the herpes and retrovirus chimeric PCR products were sequenced and the results were similar to those published previously [Jones et al., 1996. J. Virol. 70, 2460–2467]. This assay might be adopted in additional systems to detect foreign inserts at suspected genomic sites.