Bovine papillomavirus type 1 E1 replication-defective mutants are altered in their transcriptional regulation.
Bovine papillomavirus type 1 (BPV-1) is capable of replicating as a stable, high-copy-number plasmid in transformed rodent cells. The BPV-1 E1 open reading frame (ORF) encodes multiple functions involved in viral DNA replication. Mutations which disrupt the translational integrity of the E1 ORF disable the viral genome from replicating as a stable plasmid and result in the integration of the viral genome into the host chromosome generally at a low copy number. Despite the low copy number of the integrated genomes, BPV-1 E1 mutants transform rodent cells to anchorage independence very efficiently, at levels equal to or greater than that of wild-type (wt) BPV-1. Studies were performed to provide insight into why these low-copy-number, replication-defective mutants are capable of expressing an equal or greater transformation potential than wt BPV-1. Analysis of viral RNA revealed higher rates of transcription per viral genome in cells harboring E1 mutated BPV-1 DNA than in cells containing wt BPV-1 DNA. Furthermore, the levels of viral RNA mapping the P89 promoter were found to be 15- to 35-fold higher in cells transformed by E1 mutated DNAs compared with wt BPV-1 transformants. This promoter controls expression of the BPV-1 E6 transforming gene and is regulated by the viral E2 gene products. The studies presented in this report determined that the E1 mutants were perturbed in their E2 transcriptional regulation, suggesting a possible explanation for the observed P89 induction. Mutations throughout the E1 ORF, in either of the two regions previously identified as encoding distinct replication functions, were altered in viral transcription.
Lambert
P F
PF
Laboratory of Tumor Virus Biology, National Cancer Institute, Bethesda, Maryland 20892.
Howley
P M
PM
D000818:Animals; D052688:Bovine papillomavirus 1 / Q000235:genetics*; D002448:Cell Adhesion; D002472:Cell Transformation, Viral; D002478:Cells, Cultured; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D005786:Gene Expression Regulation; D009154:Mutation; D027383:Papillomaviridae / Q000235:genetics*; D010957:Plasmids; D011401:Promoter Regions, Genetic; D012367:RNA, Viral / Q000096:biosynthesis / Q000502:physiology; D014779:Virus Replication
D012367:RNA, Viral; D015500:Chloramphenicol O-Acetyltransferase