Transcriptional regulatory elements in the noncoding region of human papillomavirus type 6

We have identified three elements in the noncoding region of human papillomavirus type 6 (HPV-6) that regulate transcription when assayed in recombinant plasmids containing the bacterial gene for chloramphenicol acetyltransferase. One was a silencer that reduced expression in both a species- and tissue-dependent manner. The second was an enhancer element that was tissue specific. The third was a weak promoter that showed some tissue specificity. These elements have been localized within the noncoding region by analysis of 5'-to-3' and 3'-to-5' deletions with two HPV-6 subtypes, HPV-6e and HPV-6g. HPV-6g differs from HPV-6e by the presence of an additional copy in tandem of a 136-base-pair (bp) sequence and by an 8-bp sequence containing a 3-bp deletion. Silencer activity, assayed in plasmids with the simian virus 40 minimum promoter which were transfected into NIH 3T3 cells, could not be overcome by the enhancer activity of the simian virus 40 72-bp repeats. The 413-bp fragment A of HPV-6g showed silencer activity, while the corresponding HPV-6e fragment containing the 8-bp change did not. Enhancer activity of HPV-6g was localized to fragment C of 326 bp which contains the 136-bp repeat. Dot blot hybridizations reflected relative chloramphenicol acetyltransferase activities and demonstrated enhancer and silencer activities at the RNA level. Analysis of the interactions of these activities in naturally occurring variants should provide information on tissue specificity and regulation of gene expression of HPVs and may provide information on the mechanism of action of transcriptional regulatory elements in eucaryotic cells.