Analysis of the herpes simplex virus type 1 promoter controlling the expression of UL38, a true late gene involved in capsid assembly.

The cistrons encoding the herpes simplex virus type 1 (HSV-1) UL37 and UL38 genes are adjacent to one another but are transcribed from opposite strands of the viral DNA. The UL37 gene encodes a 1,123-amino-acid protein of unknown function, while the 465-amino-acid UL38 protein is involved in capsid assembly. Previous work from our laboratory indicated that the transcripts encoding these proteins are expressed with significantly different kinetics in productive infection. In the present communication we confirm the kinetic classes and precisely map the cap sites of the UL37 and UL38 mRNAs. A bifunctional reporter gene vector was used to demonstrate that divergent promoters control the expression of these reporter genes in trans-activation assays. The UL38 promoter is functionally separable from that controlling UL37 in a recombinant virus. We used deletion analysis to demonstrate that as few as 29 bases 5' of the mRNA cap site are adequate for full activity of the UL38 promoter in trans-activation assays. Finally, we analyzed the protein-binding properties of the UL38 promoter; several sites that form complexes containing ICP4, with clear homology to those identified in the HSV-1 gamma 42 promoter, are present. Thus, in general, the properties of this promoter are quite similar to those of other gamma promoters.