Characterization of a promoter in the E7 open reading frame of human papillomavirus type 11.

A human papillomavirus type 11 (HPV-11) early gene promoter, PE1--E4, in the E7 open reading frame and involved in the transcription of E1--E4 and E1--E4, L1 mRNAs was characterized by chloramphenicol acetyl transferase (CAT) assay, gel-shift assay, in vitro transcription, and primer extension. By CAT assay with CAT-expression plasmids containing various portions of the HPV-11 genome from nucleotide position (nt) 235 to nt 743, we identified a 112-basepair (bp) sequence (nt 632-743) that had high promoter activity and a 188-bp upstream sequence from nt 395 to nt 572 that strongly suppressed activity. The 112-bp sequence contained a 7-bp repeat (7-bp Rep) with high homology to the Sp1-binding motif (BM) in the E6 promoter of HPV-11 but lacked an identifiable TATA-box. A cellular protein other than Sp1 bound to the 7-bp Rep. Removal of a 21-bp segment (nt 632-652) containing the 7-bp Rep significantly reduced activity. By in vitro transcription assay and primer extension, one of the transcription start sites was mapped to near nt 719. These results suggested that a cellular protein that binds to the 7-bp Rep may act as an activator for PE1--E4.