Ultrastructural studies of H-1 parvovirus replication. V. Immunocytochemical demonstration of separate chromatin-associated and inclusion-associated antigens.

Electron microscopy and immunocytochrome c staining were used to define the phenotypes of several temperature-sensitive (ts) H-1 mutants. They were classified into three separate groups based on the properties of their capsids at the restrictive temperature (rT): (class 1) ts2 did not assemble capsids but produced spherical and irregular amorphous inclusions; (class 2) ts1 and ts7 exclusively synthesized empty particles which all aggregated and crystallized; and (class 3) ts8 and ts10 formed noncrystalline aggregates of empty virions, but many individual full, as well as empty, capsids were associated with euchromatin. Synthesis of progeny DNA and hemagglutinin at rT were normal for class 3 mutants, but defective for those in classes 1 and 2. The immunospecific staining patterns of these mutants indicated that the H-1 capsid proteins probably form two separate intranuclear antigens: (i) a thermostable chromatin-associated antigen present in proteins that have not formed capsids and are concentrated on heterochromatin and nucleolar-associated chromatin and (ii) a thermolabile inclusion-associated antigen found in the proteins of assembled empty capsids that compose H-1 inclusions.