Analysis of the X gene promoter of woodchuck hepatitis virus.
During the course of woodchuck hepatitis virus (WHV) replication three virus-specific mRNA transcripts that encode four essential proteins are produced. The transcripts are 3.6, 2.3, and 0.7 kb in size. The 3.6-kb transcript serves as the replicative intermediate as well as the template for translation of the nucleocapsid and polymerase proteins. The 2.3-kb mRNA serves as the template for translation of the virus envelope proteins. Both the 3.6- and 2.3-kb transcripts are polyadenylated and are readily found in the cytoplasm of infected hepatocytes. However, the 0.7-kb transcript, specific for the X gene, accumulates in the nucleus of infected cells and is polyadenylated poorly in hepatocytes. Thus, while it is likely that the 0.7-kb transcript is the template for translation of the X protein, it is possible that it also has a function at the RNA level to regulate virus replication or gene expression. In order to characterize the WHV X promoter we cloned the region of the WHV8 genome encompassing the viral enhancer through the amino terminus of the X gene into the vector pSV0CAT. We transfected Huh-7 and WLC-3 cells with the WHV X promoter construct, along with a plasmid encoding human growth hormone to control for transfection efficiency, and assayed for the presence of chloramphenicol acetyl transferase activity. We found that the WHV X promoter was about one-half as active as the well-studied simian virus 40 early or Rous sarcoma virus promoters. Next, we made a series of 5' and 3' deletion mutants and mapped the WHV X promoter to a 21-nucleotide domain (1482-GGGGAAGCTGACGTCCTTTCC-1502) which is approximately 100 bp downstream of the corresponding promoter in hepatitis B virus. Further analysis, using oligonucleotide-directed mutagenesis, demonstrated that the essential nucleotides comprising the WHV X promoter are located in a 10-nucleotide domain near the initiation codon of the X gene. Mutation of either nucleotide T at position 1490 or G at position 1491 within this domain was sufficient to reduce the level of promoter activity by 100-fold. Thus, we have defined the important nucleotides within the promoter of the WHV X transcript which is a first step in understanding the role of this transcript in WHV replication and gene expression.
Hepatitis Virus Section, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892.
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F
Sugata
H S
HS
Chen
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S
Kaneko
R H
RH
Purcell
R H
RH
Miller
D000818:Animals; D001483:Base Sequence; D017919:Hepatitis B Virus, Woodchuck / Q000235:genetics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides; D011401:Promoter Regions, Genetic; D017384:Sequence Deletion; D015534:Trans-Activators / Q000235:genetics*; D014407:Tumor Cells, Cultured; D014764:Viral Proteins / Q000235:genetics*
D009838:Oligodeoxyribonucleotides; D015534:Trans-Activators; D014764:Viral Proteins; C090237:protein X, Woodchuck hepatitis B virus