Herpes simplex virus type 1 DNA synthesis requires the product of the UL8 gene: isolation and characterization of an ICP6::lacZ insertion mutation.

We investigated the role of the herpes simplex virus type 1 UL8 gene product in viral DNA replication. First, we unambiguously fine mapped the mutation in tsS38 (complementation group 1-26) to an open reading frame, designated UL8, predicted to encode an 80-kilodalton protein. Previous studies indicated that tsS38 was capable of synthesizing low to moderate levels of viral DNA at the nonpermissive temperature (C. T. Chu, D. S. Parris, R. A. F. Dixon, F. E. Farber, and P. A. Schaffer, Virology 98:168-181, 1979); thus, it was not clear whether the UL8 gene product is essential for viral DNA synthesis. Therefore, a deletion-insertion mutation was constructed in the UL8 gene by removing most of its coding sequences and replacing them with the Escherichia coli lacZ gene under control of the viral ICP6 regulatory signals. The resulting recombinant, hr80, was propagated in helper cells (S22) which express the wild-type version of the UL8 gene, but was incapable of forming plaques in Vero cells. Furthermore, hr80 was totally defective in the synthesis of viral DNA and late proteins under nonpermissive growth conditions. These results demonstrated that the UL8 gene product is essential for viral DNA synthesis.