Characterization of the cis elements involved in basal and E2-transactivated expression of the bovine papillomavirus P2443 promoter.

Transcriptional transactivation and repression by the viral E2 proteins are important regulatory mechanisms for the papillomaviruses. In the bovine papillomavirus type 1 (BPV-1), several viral promoters can be transactivated by E2 through E2-dependent enhancer elements located in the viral long control region (LCR), including promoters involved in E2 expression itself. This report demonstrates that the BPV-1 P2443 promoter is transactivated by E2-responsive elements in the LCR and that this promoter is responsible for a major part of the expression of the E2 and E5 gene products. Characterization of the cis elements involved in P2443 regulation indicated that the single E2-binding site directly upstream of P2443 is not required for either the E2 transactivation or for any E2 repression of the basal or transactivated activity of this promoter. Therefore, cooperative interactions between E2 bound at the LCR and E2 bound near P2443 do not have any role in the regulation of this promoter. Further definition of the cis regulatory elements of this promoter indicated that a binding site for the transcriptional factor Sp1 exists directly upstream of the P2443 TATA box and is critical for the basal level of transcription from this promoter. Disruption of this Sp1 site eliminated P2443 promoter activity in transient expression assays for E2 and E5 and resulted in a loss of transforming activity when introduced into the full viral genome.