LONG-TERM PROMOTER ACTIVITY DURING HERPES-SIMPLEX VIRUS LATENCY

The ability to direct foreign gene expression from the herpes simplex virus type 1 (HSV-1) genome during an acute or latent infection is a s ubject of increasing importance in the utilization of HSV vectors for gene therapy. Little is known about the types of transcription factors present in neurons or about whether different neuronal populations wi thin a ganglion vary in their complement of these factors. With respec t to HSV 1 latency, it is pot known how or why the latency-associated transcript (LAT) promoter is able to function continually during laten cy while all other viral promoters are inactive. To further studies of these two phenomena,; we constructed seven recombinant viruses with v arious promoter constructs driving expression of the lacZ reporter gen e. Each construct was inserted into HSV-1 at the glycoprotein C locus, and recombinant viruses were evaluated for the ability to express bet a-galactosidase during acute and latent viral infections in murine dor sal root ganglia. During acute infection of murine dorsal root ganglia , the activities of the promoters varied over a wide range. Constructs containing the murine metallothionein promoter (MT1), the phosphoglyc erate kinase promoter, the Moloney murine leukemia virus long terminal repeat (LTR), or the region upstream of and including the HSV LAT cor e promoter (LAT) were active during the acute but not the latent phase of infection. The addition of transcription factor binding sites pres ent in the upstream LAT region to the MT1 and LTR promoters (LAT-MT1 a nd LAT-LTR, respectively) significantly increased acute-phase expressi on. Despite these high initial rates of transcription, of all the prom oter constructs only LAT-LTR was able to remain transcriptionally acti ve after the establishment of a latent state. Thus, the Moloney murine leukemia virus LTR provides a DNA element which functions to prevent promoter inactivation during latency. An analogous HSV long-term-expre ssion element is evidently not present in the upstream LAT promoter, i ndicating that the HSV long-term-expression function is provided by a region outside of that which gives high-level neuronal expression duri ng the acute phase of infection.