In vitro promoter activity associated with the latency-associated transcript gene of herpes simplex virus type 1

The herpes simplex virus latency-associated transcript (LAT) gene is the only viral gene that shows substantial transcriptional activity during neuronal latency. The LAT RNA produced is antisense to the mRNA of the immediate early gene ICP0, partially overlaps the ICP0 mRNA, and is suspected of playing some role in latency. Sequence analysis of the region 5' to the reported transcription start site has not revealed any high consensus RNA polymerase II promoter elements. Nonetheless, LAT RNA is transcribed in low abundance during acute infection in tissue culture. As the initial step in mapping the promoter for this latency-associated gene, we analysed the ability of different regions of the LAT gene to drive the transcription of an indicator gene in vitro. Using chloramphenicol acetyltransferase (CAT) assays, we found that the genomic region between -940 and -662 nucleotides upstream of the transcription start site of the LAT gene was most efficient at directing transcription of the indicator CAT gene in Vero cells. This suggests that the LAT promoter, or at least the promoter controlling transcription of this gene during acute infection in tissue culture, may have an unusual location of more than 662 nucleotides upstream from the reported start of RNA transcription.