Characterization of intranuclear capsids made by ts morphogenic mutants of HSV-1.

We have characterized capsids made by seven temperature-sensitive (ts) mutants of HSV-1 previously shown to be defective in viral DNA processing and packaging at the nonpermissive temperature (NPT). The empty capsids isolated from mutant-infected cells at the NPT were devoid of DNA, cosedimented in sucrose with wt B capsids, and contained the same structural proteins found in wt B capsids (W. Gibson and B. Roizman (1972). J. Virol. 10, 1044-1052). The presence of VP22a in empty capsids suggests that the processing of this protein from higher-molecular-weight precursors and its association with capsids is required, but not sufficient, for DNA encapsidation. Mutants made no detectable A capsids at the NPT, but did so at the permissive temperature (PT), suggesting that A particles are generated during or subsequent to, rather than prior to, encapsidation. In temperature-shift experiments, it was demonstrated that capsids of one of the mutants, F18, made at the NPT did not participate in DNA encapsidation when cells were subsequently shifted to the PT. Only those capsids made after temperature shift to the PT acquired viral DNA, implying that the ts mutation in F18 may lie in a gene coding for a structural protein, or in a protein involved in the processing of viral DNA.