Persistent Hz-1 virus infection in insect cells: Evidence for insertion ofviral DNA into host chromosomes and viral infection in a latent status

Persistent/latent viral infections of insect cells are a prominent though p oorly understood phenomenon. In this study, the long-term association betwe en the Hz-l virus and insect host cells, conventionally referred to as pers istent viral infection, is described. With the aid of a newly developed flu orescent cell-labeling system, we found that productive viral replication o ccurs by spontaneous viral reactivation in fewer than 0.2% of persistently infected cell lines over a 5-day period. Once viral reactivation takes plac e, the host cell dies. The persistently infected cells contain various amou nts of viral DNA, and, in an extreme case, up to 16% of the total DNA isola ted from infected cells could be of viral origin. Both pulsed-field gel ele ctrophoresis and in situ hybridization experiments showed that some of thes e viral DNA molecules are inserted into the host chromosomes but that the r est of viral DNA copies are free from host chromosomes. Thus, Hz-1 virus is the first nonretroviral insect virus known to insert its genome into the h ost chromosome during the infection process. These data also suggest that t he previously described persistent infection of Hz-l virus in insect cells should be more accurately referred to as latent viral infection.