The herpes simplex virus type 1 (HSV-1) a proteins ICP4, ICPO, and ICP27 are transacting proteins which affect HSV-1 gene expression. To investigate potential interactions between these a products and to determine the specificity of action of the a proteins in combination with each other compared with their activities individually, we performed a series of transient-expression assays. In these assays we used plasmids containing the a genes encoding ICP4, ICPO, and ICP27 either singly or in combination as effectors and HSV-1 genes of different kinetic classes and heterologous genes as targets. The HSV-1 targets consisted of promoter-regulatory domains from a (ICPO and ICP27), 0 (thymidine kinase and alkaline exonuclease), P-y (glycoprotein D, glycoprotein B, and VP5), and y (glycoprotein C) genes, each fused to the chloramphenicol acetyltransferase (CAT) gene. The heterologous target genes consisted of the simian virus 40 early promoter with enhancer and the Rous sarcoma virus long terminal repeat promoter and enhancer each fused to the CAT gene. Target

The herpes simplex virus type 1 (HSV-1) a or immediate-early proteins ICP4 (IE175), ICPO (IE110), and ICP27 (IE63) are transacting proteins which affect HSV-1 gene expression. We previously showed that ICP27 in combination with ICP4 and ICPO could act as a repressor or an activator in transfection assays, depending on the target gene (R. E.

A herpes simplex virus type 1 variant [C239(TK-)] harboring a deletion in the thymidine kinase (TK) gene was assessed for capacity to establish latent infections. Outbred Swiss Webster mice were inoculated on both hind footpads, and numbers of neurons expressing latency-associated transcript and amounts of viral DNA in latently infected lumbosacral spinal ganglia were scored. C239(TK-) established levels of latent infection that were only slightly lower than those found for either a TK rescued variant of this agent or the parent wild-type KOS. However, in contrast to the TK+ viruses, C239(TK-) could not be reactivated when spinal ganglia were cultured in vitro. The results presented show that expression of the viral TK gene plays no major role in establishment of the latent state but that it functions during reactivation of latent virus from explanted ganglia maintained in vitro.

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Within the polyprotein encoded by hepatitis C virus (HCV), the minimum components required for viral RNA replication lie in the NS3-5B region, while virion assembly requires expression of all virus components. Here, we have employed complementation systems to examine the role that HCV polyprotein precursors play in RNA replication and virion assembly. In a trans-complementation assay, an HCV NS3-5A polyprotein precursor was required to facilitate efficient complementation of a replicationdefective mutation in NS5A. However, this requirement for precursor expression was partially alleviated when a second functional copy of NS5A was expressed from an additional upstream cistron within the RNA to be rescued. In contrast, rescue of a virion assembly mutation in NS5A was more limited but exhibited little or no requirement for expression of functional NS5A as a precursor, even when produced in the context of a second replicating helper RNA. Furthermore, expression of NS5A alone from an additional cistron within a replicon construct gave greater rescue of virion assembly in cis than in trans. Combined with the findings of confocal microscope analysis examining the extent to which the two copies of NS5A from the various expression systems colocalize, the results point to NS3-5A playing a role in facilitating the integration of nonstructural (NS) proteins into viral membrane-associated foci, with this representing an early stage in the steps leading to replication complex formation. The data further imply that HCV employs a minor virion assembly pathway that is independent of replication. IMPORTANCEIn hepatitis C virus-infected cells, replication is generally considered an absolute prerequisite for virus particle formation. Here we investigated the role that the viral protein NS5A has in both replication and particle assembly using complementation assays and microscopy. We found that efficient rescue of replication required NS5A to be expressed as part of a larger polyprotein, and this correlated with detection of NS5A at sites where replication occurred. In contrast, rescue of particle assembly did not require expression of NS5A within the context of a polyprotein. Interestingly, although only partial restoration of particle assembly was possible by complementation, that proportion that could be rescued benefitted from expressing NS5A from the same RNA being packaged. Collectively, these findings provide new insight into aspects of polyprotein function. They also support the existence of a minor virion assembly pathway that bypasses replication.