A composite polyadenylation signal with TATA box function.
A variant polyadenylation signal, which is conserved and employed by mammalian hepadnaviruses, has a sequence resembling that of the TATA box. We report here that this composite box manifests all the promoter characteristics. It binds effectively TATA-binding protein with TFIIB and TFIIA in a synergistic manner. This capacity, however, is lost when the box is converted to a canonical and simple poly(A) signal. Furthermore, we show that it has promoter activity and supports transcription of reporter genes preferentially in liver-derived cells, a characteristic behavior of the hepatitis B virus (HBV) promoters. In addition, we show that the HBV noncanonical poly(A) signal supports transcription initiation from the viral genome, suggesting that it is a genuine promoter, possibly of the polymerase/reverse transcriptase gene. Finally, we found that this deviant poly(A) signal is crucial for HBV replication since a viral mutant with a canonical poly(A) box is impaired in replication. Our data, therefore, raise the interesting and novel possibility that a composite poly(A) box might have a dual function. At the level of DNA it functions as a promoter to initiate transcription, whereas at the level of RNA it serves as a poly(A) signal to process RNA. An interesting outcome of this strategy of gene expression is that it provides a novel mechanism for the synthesis of an approximately genome length transcript.
Paran
N
N
Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel.
Ori
A
A
Haviv
I
I
Shaul
Y
Y
D001483:Base Sequence; D001665:Binding Sites; D006528:Carcinoma, Hepatocellular; D015967:Gene Expression Regulation, Viral; D017930:Genes, Reporter; D006515:Hepatitis B virus / Q000235:genetics* / Q000502:physiology; D006801:Humans; D008113:Liver Neoplasms; D008969:Molecular Sequence Data; D011061:Poly A / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012194:RNA-Directed DNA Polymerase / Q000235:genetics; D011994:Recombinant Proteins / Q000096:biosynthesis; D016385:TATA Box; D035561:Transcription Factor TFIIA; D035581:Transcription Factor TFIIB; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured; D014779:Virus Replication
D011994:Recombinant Proteins; D035561:Transcription Factor TFIIA; D035581:Transcription Factor TFIIB; D014157:Transcription Factors; D011061:Poly A; D012194:RNA-Directed DNA Polymerase