Evidence that less-than-full-length pol gene products are functional in hepadnavirus DNA synthesis.
Duck hepatitis B virus mutants containing frameshift or stop codon mutations in a portion of the viral pol gene separating the terminal protein and reverse transcriptase domains had a leaky phenotype and, depending on the location and type of mutation, synthesized up to 10% as much viral DNA as did the wild type. This region of the pol gene had previously been reported to be refractory to missense mutations; in fact, the leakiness of most of our mutants appeared attributable to translational suppression, which would also be expected to introduce amino acid changes. However, at least one mutant (pH1093 + 2), which was ca. 10% as active as the wild type, appeared to use a novel pathway to express the viral pol gene. Our analyses indicated that pH1093 + 2 synthesized the viral reverse transcriptase as a fusion protein with the amino-terminal portion of the pre-S envelope protein. Thus, in this case, the products of the terminal-protein and reverse transcriptase domains of the pol gene would function as separate protein species, though perhaps noncovalently joined in a dimeric structure during assembly of DNA replication complexes. Evidence was also obtained that was consistent with the idea that the wild-type pol gene may, at least in certain instances, be expressed as functional, subgenic polypeptides.
Wu
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Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111.
Condreay
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LD
Coates
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Aldrich
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Mason
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D001483:Base Sequence; D002478:Cells, Cultured; D003062:Codon / Q000235:genetics; D004279:DNA, Viral / Q000096:biosynthesis*; D016368:Frameshift Mutation; D015684:Gene Products, pol / Q000235:genetics / Q000378:metabolism*; D015751:Genes, pol; D005816:Genetic Complementation Test; D015611:Hepatitis B Virus, Duck / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D010641:Phenotype; D014176:Protein Biosynthesis; D012194:RNA-Directed DNA Polymerase / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014162:Transfection
D003062:Codon; D004279:DNA, Viral; D015684:Gene Products, pol; D011993:Recombinant Fusion Proteins; D012194:RNA-Directed DNA Polymerase