A constitutive enhancer in the bovine papillomavirus upstream regulatory region shares genetic elements with the viral P1 promoter

The bovine papillomavirus upstream regulatory region represents a common element in the regulation of transcription from the five early viral promoters. We have determined the sequences required for transcription from the viral P1 promoter, which is located at the 5' end of the upstream regulatory region. In vitro transcription from P1 requires a 123-bp fragment (nucleotides 7153 to 7275; -33 to +90) consisting of an upstream TATA-like sequence as well as an unidentified protein which binds to sequences immediately downstream of the initiation site. In vivo, this promoter requires additional downstream sequences (to position +160; nucleotide 7345) for maximal activity but does not require any additional DNA sequence upstream of a putative TATA box. Four regions within the downstream sequence from +9 to +160 are protected from DNase I digestion by proteins present in a HeLa cell extract. The presence of these sites correlates with the level of P1 activity. A constitutive enhancer maps to this same region, and mutations in this enhancer have been shown to affect downstream promoters. Deletion analysis indicates that the same sequences are required by both the P1 promoter and the constitutive enhancer, suggesting that the same proteins function in both activities.