Transactivating function and expression of the x gene of hepatitis B virus.
OBJECTIVE
The x gene of hepatitis B virus encodes a transactivating factor of 154 amino acids, termed HBx, which stimulates transcription of multiple viral and cellular genes. The transactivating function is probably associated with a tumorigenic potential of HBx, since x gene sequences, encoding functional HBx, have been repeatedly found integrated into the genome of liver carcinoma cells.


METHODS
To identify the transactivating domain of HBx, we constructed x gene plasmids encoding full length HBx or HBx fragments. We determined their transactivating function after cotransfection of cells, along with a plasmid that contains a reporter gene driven by the SV40 early promoter/enhancer region.


RESULTS
Our results demonstrate that a 95-amino acid fragment of HBx, encompassing amino acids 49 to 143, contains all the elements that are required for the transactivating function. Within this fragment a sequence element, encompassing amino acids 107 to 130, which contains a relatively high number of amino acids with charged side chains, appears to be crucial for the stimulation of gene expression. The influence of deletion mutations on x mRNA steady-state levels and HBx stability was examined. In essence, stable RNA and protein were produced if at least codons 1-82 or 70-154 were present in the deletion plasmids.


CONCLUSIONS
This finding strongly suggests that the deletion of functional domains between codons 49 and 143, but not an instability of RNA and/or protein, was critical for the loss of transactivation.
Department of Virus Research, Max-Planck-Institut für Biochemie Martinsried, Germany.
M
M
Renner
A
A
Haniel
E
E
Bürgelt
P H
PH
Hofschneider
W
W
Koch
D015152:Blotting, Northern; D015153:Blotting, Western; D004273:DNA, Neoplasm / Q000032:analysis / Q000235:genetics; D004279:DNA, Viral / Q000032:analysis / Q000235:genetics; D019084:Fluorescent Antibody Technique, Indirect; D017353:Gene Deletion; D015967:Gene Expression Regulation, Viral; D005814:Genes, Viral / Q000235:genetics* / Q000502:physiology; D006515:Hepatitis B virus / Q000235:genetics*; D006801:Humans; D008113:Liver Neoplasms / Q000737:chemistry / Q000235:genetics / Q000473:pathology; D009154:Mutation; D010957:Plasmids; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
D004273:DNA, Neoplasm; D004279:DNA, Viral; D012333:RNA, Messenger