Herpes simplex virus 1 mutant deleted in the alpha 22 gene: growth and gene expression in permissive and restrictive cells and establishment of latency in mice

Abstract

R325-.beta.TK+, a herpes simplex virus 1 mutant carrying a 500-base-pair deletion in the .alpha.22 gene and the wild-type (.beta.) thymidine kinase (TK) gene, was previously shown to grow efficiently in HEp-2 and Vero cell lines. It is reported that in rodent cell lines exemplified by the Rat-1 line, plating efficiency was reduced and growth was multiplicity dependent. A similar multiplicity dependence for growth and lack of virus spread at low multiplicity was seen in resting, confluent human embryonic lung (HEL) cells. The shutoff of synthesis of .beta. proteins was delayed and the duration of synthesis .gamma. proteins was extended in R325-.beta.TK+-infected HEL cells relative to cells infected with the wild-type parent, but no significant differences were seen in the total accumulation of viral DNA. To quantify the effect of late (.gamma.2) gene expression, a recombinant carrying the deletion in the .alpha.22 gene and a .gamma.2-TK gene (R325-.gamma.2TK) was constructed and compared with a wild-type virus (R3112) carrying a chimeric .gamma.2-TK gene. In Vero cells, the .gamma.2-TK gene of R325-.gamma.2 TK was expressed earlier than at the same level as the .gamma.2-TK gene of R3112. In the confluent resting HEL cells, the expression of the .gamma.2-TK gene of the .alpha.22- virus was grossly reduced relative to that of the .alpha.22+ virus. EM studies indicated that the number of intranuclear capsids of R325-.beta.TK+ virus was reduced relative to that of the parent virus in resting confluent HEL cells, but the number of DNA-containing capsids was higher. Despite its grossly reduced neurovirulenece on intracerebral inoculation in mice, R325-.beta.TK+ virus was able to establish latency in mice. Thus, the .alpha.22 gene affects late (.gamma.2) gene expression, and a host cell factor complements that function of the .alpha.22 gene to a greater extent in HEp-2 and Vero cells than in confluent, resting HEL cells.