The herpes simplex virus type 1 genome contains four open reading frames (ORFs) which are predicted to encode hydrophobic proteins with the potential to cross a membrane several times. The products of these genes (genes UL10, UL20, UL43 and UL53) have not previously been identified. To investigate the role of these proteins in the virus life cycle, we attempted to inactivate the genes individually by inserting the lacZ gene from Escherichia coli within the ORFs. Using this approach we have isolated insertion mutants for UL10 and UL43, as well as a deletion mutant lacking the majority of the UL43 ORF. The growth of the UL10-lacZ virus was slightly impaired in tissue culture compared to that of the wild-type virus parent, whereas the growth of the UL43 mutants was indistinguishable from that of wild-type virus. Furthermore, deletion of the majority of the UL43 ORF did not impair the ability of the virus to replicate in vivo at the periphery, or to spread to and replicate within the nervous system, in a mouse ear model. Repeated attempts to isolate lacZ insertion mutants for UL20 and UL53 were unsuccessful, suggesting that these genes may be essential for virus growth, at least in tissue culture. Using antipeptide sera, the products of genes UL10 and UL20 have been detected.

SUMMARYThe genes of herpes simplex virus type 1 (HSV-1) can be divided into at least three temporally regulated groups termed immediate early (IE), early and late. We have Studied in detail the expression of a member of the late class of genes, US11, which encodes a polypeptide of apparent molecular weight 21K. Highly specific and sensitive probes were used to monitor US1 t RNA and protein synthesis during HSV-1 infection of tissue culture cells in the presence and absence of phosphonoacetic acid, an inhibitor of viral DNA replication. The results were compared with a similar study of the products of a delayed early gene, US6, encoding glycoprotein D (gD). It was found that the patterns of RNA and protein synthesis from US11 were significantly different to those of gD. US11 products appeared later and accumulated until late in infection, while gD RNA was significantly reduced at late times. In the presence of the inhibitor of DNA synthesis, USll gene expression was reduced 50-to 100-fold while gD expression was reduced five-to tenfold. We conclude that US11 behaves as a true late gene during HSV-1 infection. However, the use of sensitive assays, which allowed the detection of very low levels of USI 1 gene products under conditions designed to eliminate DNA replication, brings into question the absolute requirement for DNA replication for the expression of a true late HSV-1 gene. These results are discussed in terms of current models for the regulation of late gene expression.

We have investigated whether herpes simplex virus (HSV) contains structural polypeptides which are modified by myristic acid. We demonstrate that herpes simplex virions contain a family of myristylated proteins, Mr approximately 13,000 to 16,000. These were mapped, using HSV-1/HSV-2 intertypic recombinants, to 0.130 to 0.204 map units on the virus genome. Using anti-peptide sera, raised against the carboxyterminus of the predicted UL11 gene product, we have established that the myristylated virion polypeptides are products of the viral gene UL11.

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