GROWTH OF THE PARVOVIRUS MINUTE VIRUS OF MICE MVMP3 IN EL4 LYMPHOCYTES IS RESTRICTED AFTER CELL ENTRY AND BEFORE VIRAL-DNA AMPLIFICATION - CELL-SPECIFIC DIFFERENCES IN VIRUS UNCOATING IN-VITRO

Two murine parvoviruses with genomic sequences differing only in 33 nu cleotides (8 amino acids) in the region coding for the capsid proteins show different host cell specificities: MVMi grows in EW T lymphocyte s and MVMp3 grows in A9 fibroblasts. In this study we compared the cou rses of infections with these two viruses in EL4 cells in order to inv estigate at which step(s) the infection process of MVMp3 is interrupte d, The two viruses bound equally well to EW cells, and similar amounts of MVMi and MVMp3 input virion DNA appeared in the nuclear fractions of EW cells 1 h after infection, However, double-stranded replicative- form (RF) DNA of the two viruses appeared at different times, at 10 h postinfection with MVMi and at 24 h postinfection with MVMp3. The amou nt of MVMp3 RF DNA detected at 24 h was very small because it was prod uced only in a tiny subset of the population of EU cells that proved t o be permissive for MVMp3. Replication of double-stranded viral DNA in EU cells was measured after transfection of purified RF DNA, cloned v iral DNA, and cloned viral DNA with a mutation preventing synthesis of the capsid proteins, In each of these cases, DNA replication was comp arable for MVMi and MVMp3. Production of virus particles also appeared to be similar after transfection of the two types of RF DNA into EW c ells, Conversion of incoming P-32-labeled single-stranded MVM DNA to P -32-labeled double-stranded RF DNA was detected only after RF DNA ampl ification, indicating that few molecules serve as templates for viral DNA amplification, We showed that extracts of EW cells contain a facto r which can destabilize MVMi virions but not MVMp3 by testing the sens itivity of viral DNA to DNase and by CsCl gradient analyses of viral p articles, We therefore conclude that the MVMp3 life cycle is arrested after the transport of virions to the nucleus and prior to the replica tion of RF DNA, most likely at the stage of viral decapsidation.