Effect of genomic location on expression of beta-galactosidase mRNA controlled by the herpes simplex virus type 1 UL38 promoter.

To examine the effect of genomic location on the details of expression of selected herpes simplex virus promoters, we have constructed recombination vectors for placing such promoters controlling the beta-galactosidase reporter gene into two regions of the viral genome lacking any nearby promoter or regulatory elements. The first vector generates the promoter-beta-galactosidase reporter gene inverted within the locus of the gC (UL44) translational reading frame; the second replaces the LAT promoter and the first 600 bases of the primary transcript in both copies of the RL region. These locations were chosen to obviate any possible influence of upstream but noncontiguous heterologous or homologous DNA sequence elements upon promoter activity. When the reporter gene controlled by the strict late (gamma) UL38 promoter was placed in the gC location, it was significantly less active than in its normal location; in contrast, promoter activity was comparable to wild-type values when the promoter was recombined into the RL region. The low level of activity in the gC location could be partially alleviated by the incorporation of additional DNA sequences upstream of the UL38 promoter. Despite the effect of genomic location upon the level of expression, the kinetics of expression in either location mirrors the wild-type UL38 strict late kinetics of expression. Finally, we used deletional analysis to demonstrate that no more than 29 bases of DNA sequence 5' of the mRNA cap site are required for promoter activity in either location; this result is consistent with earlier results of transient-expression assays and indicates that the UL38 promoter shares general features with other strict late (gamma) herpes simplex virus promoters.