Regulation of herpes simplex virus immediate early gene expression.

Herpes Simplex virus (HSV) is responsible for a number of diseases which range in severity from subclinical infection to lethal encephalitis. The most common human illnesses caused by HSV are the recurrent common cold sore and genital herpes. Following infection of human individuals with HSV the virus replicates lytically in peripheral epithelial cells causing mucocutaneous lesions before infecting neurons where it is able to establish a latent infection in which the viral genome remains transcriptionally quiescent in an apparently healthy neuron [ I ] . Under certain conditions including axotomy. UV light, hypothermia, elevations in cyclic AMP levels or nerve growth factor deprivation, HSV can be stimulated to reactivate from latency and can enter the lytic cycle [2]. The ability of HSV to enter into a latent state in sensory neurons and then repeatedly reactivate and spread to other hosts is a primary reason that HSV is such a prevalent human pathogen. The failure of the viral lytic cycle in sensory neurons and the establishment of latent infection, is dependent upon failure of viral IE gene transcription following infection resulting in the lytic cycle being aborted at an early stage. Immortalised neuronal cell lines have been used to show that the failure of IE gene transcription is associated with the binding of the POU domain transcription factor to the octamer-related TAATGARAT motif in the IE promoters resulting in inhibition of IE activity [3]. We have investigated IE gene expression in cultured primary sensory neurons. To determine if the expression of the IE gene is blocked by the binding of a neuronal specific repression protein to the TAATGARAT motif. The ICP4 promoter [4] was linked to the CAT gene and co-transfected into primary cultures of sensory neurons with increasing concentrations of plasmid containing the TAATGARAT motif. CAT activity was assayed by the method of Gorman 151 on cell extracts which had been equalised for protein content. 0