1887

Abstract

Besides the three essential genes encoding the envelope, core and polymerase proteins, all mammalian hepadnaviruses examined to date contain a fourth gene which is referred to as the -gene. This gene is believed to encode a transcriptional transactivator which positively regulates viral gene expression. Attempts to detect X-protein or in tissue culture lead to varying results. Whereas some groups could detect a protein of the expected size, other groups did not. To establish optimal conditions for the isolation of the human hepatitis B virus X-protein, we introduced a recognition site for protein kinase A into the -gene. Upon phosphorylation with radioactive ATP, this modified X-protein can be detected with very high specificity and sensitivity. Tissue culture experiments showed that X-protein expressed from a cytomegalovirus-driven plasmid is not soluble in non-ionic detergent but rather has to be extracted from the cell pellet by boiling with SDS at a slightly alkaline pH. This method was then used to examine the organs of several transgenic mouse lines which expressed the modified -gene under control of the authentic promoter. The data show that expression of the -gene and subsequent biosynthesis of the X-protein is not tissue-specific but rather can occur in most organs.

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1999-09-01
2021-03-05
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