J. gen. Virol. (1982), 60, 87-97. Printed in Great Britain Key words: nucleocapsMs/persistence/Dlparticles/rabies 87 Analysis of Viral and Defective-Interfering Nucleocapsids in Acute and Persistent Infection by Rhabdoviruses By ELIZABETH A. GRABAUt AND JOHN J. HOLLAND* Department of Biology, C-016 University of California, San Diego, La Jolla, California 92093, U.S.A. (Accepted 14 December 1981) SUMMARY We have isolated and characterized the RNA of intracellular virus nucleocapsids recovered from a number of cell cultures persistently infected with rabies virus or vesicular stomatitis virus (VSV). VSV persistent infections in BHK21, L cells and Aedes albopictus (mosquito) cells generally showed the presence of large amounts of defective-interfering (DI) nucleocapsid RNA and much smaller amounts of standard (B) nucleocapsid RNA. Persistent infections of BHK21 cells by two rabies virus strains, challenge virus standard (CVS-11) or HEP-Flury, were followed for several months during which time the ratio of DI to B nucleocapsid RNA cycled dramatically. We also observed coordinated fluctuations in the absolute amount of incorporation of [3H]uridine into virus nucleocapsid RNA. Total incorporation was generally highest following a decrease in the relative amount of DI nucleocapsid RNA synthesis. At no time were DI nucleocapsids absent in any of the persistently infected cultures. INTRODUCTION Many different viruses are capable of establishing long-term persistent infections in vitro and in vivo (for review, see Stevens et al., 1978). Persistent infections by rhabdoviruses, a group of enveloped, negative-strand RNA viruses, are among the best-studied systems. Holland & Villarreal (1974) showed that vesicular stomatitis virus (VSV) readily established persistent infection of BHK21 cells but required the addition of homologous defective- interfering (DI) particles to do so. DI particles were necessary to attenuate the virulence of VSV for the host cell. These persistently infected cells continually shed variable, low levels of standard infectious virus (B virions) and DI virions into the culture medium. Further analysis of the cultures showed that DI particles were constantly present but that the populations of both standard and DI virus were continuously changing as determined by T 1 oligonucleotide mapping (Holland et al., 1979). Wiktor & Clark (1972) showed that rabies virus could also establish persistent infection of tissue culture cells. The ability of rabies virus to generate DI particles was demonstrated by Crick & Brown (1974). The rapid generation of DI particles and the slow growth of the virus give rise to persistent infection by rabies virus whether or not large numbers of DI particles are added to the inoculum (Holland et al., 1976b). Kawai et al. (1975) failed to detect any interferon in rabies virus persistent infection and were able to isolate DI particles from these cultures. They observed a cyclical production of both standard and DI virions by the persistently infected cells and concluded that DI particles play an important role in establishing and maintaining persistent infection by rabies virus. They also found a changing "~ Presentaddress:Departmentof Biology, University of Utah, Salt Lake City, Utah 84112, U.S.A. 0022-1317/82/000-4904 $02.00 © 1982 SGM