Bovine papillomavirus transcriptional regulation: localization of the E2-responsive elements of the long control region

Abstract

The long control region (LCR) of the bovine papillomavirus type 1 genome can function as a conditional transcriptional enhancer which can be specifically trans-activated by the viral E2 gene product. To precisely map the target(s) of this trans-activation, BAL 31 exonuclease was used to generate two overlapping series of deleted DNA segments through the LCR. These fragments were assayed for their ability to activate transcription from the enhancer-deleted simian virus 40 early promoter of pA10CAT in the presence or absence of the viral E2 gene product. Two different E2-responsive elements were localized within the LCR. The major target for E2 trans-activation (E2-responsive element 1) was mapped to a 196-base-pair fragment between nucleotides 7611 and 7806, just upstream from promoters P7940 and P89. Further deletions which destroyed or impaired enhancer function revealed that the ACCN6GGT sequence motifs at each end of E2-responsive element 1 are critical components of this element. Primer extension analysis of RNA extracted from acute transfections with plasmids containing the bovine papillomavirus type 1 LCR driving the CAT gene revealed that each of the P7940 and P89 promoters is responsive to E2 trans-activation.