Morphogenesis of nuclear inclusions and virus capsids in HEL cells infected with temperature-sensitive mutants of human cytomegalovirus.

The morphogenesis of nuclear inclusions and virus capsids in human embryonic lung cells infected with ts mutants of human cytomegalovirus at permissive (34 degrees C) and non-permissive (39 degrees C) temperatures was studied by indirect immunofluorescence (IF) and electron microscopic analyses and compared with the morphogenesis of these structures in wild-type virus infection with or without phosphonoacetate. Mutants tested belonged to five different complementation groups: two groups were DNA- (those unable to synthesize virus DNA at 39 degrees C) and the others were dna+. Based on the previous finding that the electron-dense, reticular nuclear inclusions (EM-NI) observed by the thin-section analysis correspond with nuclear inclusions (IF-NI) detected by the indirect IF staining (i.e. they occupy the same space in the nucleus), the following conclusions were obtained in ts mutant infection at 39 degrees C: (i) the formation of EM-NI, IF-NI and virus capsids requires replication of virus DNA. (II) The formation of EM-NI is not necessarily accompanied by the formation of IF-NI; EM-NI itself is not IF-positive unless it acquires virus-specific late antigens. (iii) The assembly of virus capsids occurs only in those cells in which EM-NI is formed; however, it can occur without the formation of IF-NI. (iv) Virus capsids assembled are not the major antigens responsible for the fluorescence of nuclear inclusions.