Site-specific cleavage/packaging of herpes simplex virus DNA and the selective maturation of nucleocapsids containing full-length viral DNA

Abstract

Defective genomes present in serially passaged herpes simplex virus (HSV) stocks consist of tandemly arranged repeat units containing limited sets of the standard virus DNA sequences. Invariably, the HSV defective genomes terminate the right (S component) terminus of HSV DNA. Because the oligomeric forms can arise from a single repeat unit, the defective genomes appear to arise by a rolling circle mechanism of replication. Defective genomes packaged in viral capsids accumulating in the nuclei and in mature virions (enveloped capsids) translocated into the cytoplasm of cells infected with serially passaged virus were studied. Upon electrophoresis in agarose gels, the defective genomes prepared from cytoplasmic virions comigrated with nondefective standard virus DNA (MW 100 .times. 106). DNA prepared from capsids accumulating in nuclei consisted of both full-length defective virus DNA molecules and smaller DNA molecules of discrete sizes, ranging in MW from 5.5-100 .times. 106. These smaller DNA species consisted of different integral numbers (from 1 to .apprx. 18) of defective genome repeat units and terminated with sequences corresponding to the right terminal sequences of HSV DNA. Apparently, sequences from the right end of standard virus DNA contain a recognition signal for the cleavage and packaging of concatemeric viral DNA. The sequence-specific cleavage is either prerequisite for or occurs during the entry of viral DNA into capsid structures. DNA molecules significantly shorter than full-length standard viral DNA apparently can become encapsidated within nuclear capsids provided they contain the cleavage/packaging signal. Capsids containing DNA molecules significantly shorter than standard virus DNA are not translocated into the cytoplasm.