A composite polyadenylation signal with TATA box function

Area of Science:

• Virology
• Molecular Biology
• Gene Regulation

Background:

• Mammalian hepadnaviruses utilize a conserved polyadenylation signal with TATA box-like features.
• The precise function of this noncanonical polyadenylation signal in viral gene expression and replication remains incompletely understood.

Purpose of the Study:

• To investigate the promoter characteristics and functional significance of the variant polyadenylation signal in mammalian hepadnaviruses.
• To elucidate the dual role of this sequence in transcription initiation and RNA processing.

Main Methods:

• Electrophoretic mobility shift assays (EMSA) to assess protein binding.
• Reporter gene assays in liver-derived cells to evaluate promoter activity.
• Analysis of viral mutants to determine the impact on replication.

Main Results:

• The composite polyadenylation signal binds TATA-binding protein, TFIIB, and TFIIA synergistically, exhibiting promoter characteristics.
• This signal supports transcription preferentially in liver cells and initiates transcription from the viral genome.
• A mutation to a canonical polyadenylation signal impairs hepatitis B virus replication, highlighting the importance of the deviant signal.

Conclusions:

• The noncanonical polyadenylation signal in hepadnaviruses functions as a dual-purpose element: a promoter for transcription initiation and a polyadenylation signal for RNA processing.
• This dual function represents a novel gene expression strategy, potentially facilitating the synthesis of genome-length transcripts and impacting viral replication.