Human papillomavirus type 8 contains cis-active positive and negative transcriptional control sequences

Human papillomavirus type 8 (HPV-8) is one aetiological agent of macular and flat wart-like lesions in patients with epidermodysplasia verruciformis and appears to be closely linked to skin carcinogenesis. A 1.2 kb region of the genome, which was previously shown to contain a viral E2-dependent enhancer, was progressively shortened from both ends with Bal 31. The resulting fragments were tested for their ability to stimulate chloramphenicol acetyltransferase (CAT) expression from the simian virus 40 (SV 40) promoter. This analysis showed a complex interaction between cis-active, positive and negative control elements located throughout the non-coding region and the flanking reading frames. Two separate positively acting sequences significantly stimulated expression only in cooperation with a third region, which led to 12-fold, E2-dependent enhancement on its own. A major negative element was not only active in the context of HPV-8 sequences, but also down-regulated SV40 enhancer-promoter-driven CAT expression when cloned downstream of the transcription unit. It acted at the transcriptional levels as shown by RNase protection assays and can therefore be regarded as a cis-acting silencer of transcription.