Structure, DNaseI hypersensitivity and expression of integrated papilloma virus in the genome of HeLa cells

Abstract

Three integrated copies of human papilloma virus-18 (HPV-18) have been identified in HeLa DNA as HindIII bands. HPV-18 has no HindIII restriction site in its genome. The three segments: A, 8.4 kb; B, 7.9 kb and C, 5.8 kb, have an incomplete viral genome. All of them have most of the 1.1-kb BamH1 non-coding fragment of HPV-18, which seems to contain the viral origin of replication and regulatory elements. Two of the segments (A and B) have a common 5'-end break-point in the viral genome within the L2 open reading frame (ORF). In both segments the second early transcriptional unit of the virus (E6, E7 and E1) is structurally conserved in a new environment. The 3'-end break-point for segments A and B is within the E2 ORF. Segment C has the L2 and L1 ORF but none of the genes of the early region. Segments A and B have a specific DNaseI-hypersensitive site located in the E7/E1 region. The nucleotide sequence of this region has twelve papova virus enhancer-like consensus sequence (5'-TACCACANTA-3') and a double inverted repeat with fixed spacing capable of forming a hairpin loop. Two viral RNA transcripts of 4.8 kb and 1.7 kb have been detected in poly(A)-rich RNA. The larger transcripts hybridizes to E6, E7 and E1 ORFs as well and has 2.4 kb of host sequence in its 3' end. The smaller transcript hybridizes with E6 and E7 ORFs and the beginning of E1, the final 0.7 kb of E1 are not detectable. No transcripts have been detected carrying E2, E4, E5, L2 and L1 ORF sequences. The transcripts are derived from segments A or B. Segment C is not transcriptionally competent.