Transcriptional control signals in the genome of bovine papillomavirus type 1.

Papillomaviruses cause benign tumours in their natural hosts, which, in some cases, become foci for the appearance and spread of malignant carcinomas. It is therefore of considerable interest to analyse the strategy of gene expression of this group of viruses. Towards this end, we have used a generally applicable technique, in which we monitor the ability of DNA fragments to induce the expression of an inactive thymidine kinase (tk) gene, from which the promoter region has been deleted. Using this approach we now report for the first time the location of four transcriptional control sequences in the early region of the genome of bovine papillomavirus type 1 (BPV-1). Two of the sequences with the characteristics of 'promoter' elements are located proximal to the putative 5' leaders of the early genes. The third sequence is located within the region coding for the main body of the early transcripts, and the fourth within the region spanning the 3' end of the early open reading frames and the 5' end of the late ones. The fourth sequence displays the characteristics of an 'enhancer' element; however, unlike previously described 'enhancers', it is located three to five kilobases (kb) away from the first two promoters and to the 3' side of the third element.