Expression of the feline herpesvirus type 1 ICP4 gene is controlled by two alternative promoters

Feline herpesvirus type 1 (FHV-1) produces a single 5.4 kb immediate-early (IE) transcript encoding FHV-1 ICP4 which acts as a trans-acting factor [Kawaguchi et al. (1994) Virology 204: 430-435]. Our earlier study has shown that the FHV-1 IE transcript is spliced in the leader region and the FHV-1 IE gene product (ICP4) down-regulates its own promoter through the region which includes its transcription initiation site [Kawaguchi et al. (1996) J Vet Med Sci 58: 715-721]. Here we investigated FHV-1 ICP4 gene expression throughout FHV-1 productive infection and demonstrated that (i) a novel promoter is located downstream of the IE promoter and an early transcript is transcribed from this promoter region, (ii) a negative regulatory element, which is composed of a 20 bp direct repeat unit repeated 20 times, is located between the two promoters and the repeat unit shows high homology to a motif called direct repeat 2 in "a" sequence of herpes simplex virus type 1, (iii) the IE promoter and synthesis of the IE mRNA appear to be turned off after IE phase and the second promoter becomes active during early and late stages, and (iv) a gene product expressed only by the second promoter also possesses regulatory function. These findings indicate that expression of the FHV-1 ICP4 gene is alternatively regulated by the two promoters.