Translational modulation in hepatitis B virus preS-S open reading frame expression.

Area of Science:

• Virology
• Molecular Biology
• Cell Biology

Background:

• The hepatitis B virus (HBV) preS-S open reading frame (ORF) encodes essential viral proteins.
• Understanding the translational regulation of HBV ORF expression is crucial for viral pathogenesis research.

Purpose of the Study:

• To investigate the translational regulation of HBV preS-S ORF variants.
• To analyze the role of start codon context and cis-acting elements in protein synthesis.
• To elucidate the mechanism of preS-mediated endoplasmic reticulum (ER) retention.

Main Methods:

• Expression of HBV preS-S ORF variants in vivo (HepG2 cells) and in vitro (rabbit reticulocyte lysate).
• Analysis of large, middle (M), and major (S) protein synthesis ratios.
• Site-directed mutagenesis to alter start codon positions and regulatory sequences.
• Construction of chimeric envelope polypeptides to study ER retention.

Main Results:

• The AUG sequence context significantly influences translational initiation, consistent with the ribosome scanning model.
• The 2.4 kb preS-S mRNA is predominantly translated from AUG1, while the 2.1 kb mRNA can utilize AUG2 and/or AUG3.
• Internal AUG initiation in the 2.4 kb RNA is possible, but cis-repression elements near AUG2 did not affect internal AUG utilization in vitro.
• A preS1-derived sequence mediates ER retention of M protein, independent of glycosylation, suggesting an intra-ER lumenal function.

Conclusions:

• Translational control of HBV preS-S mRNA is primarily determined by the sequence context of start codons.
• The preS1 sequence acts as a signal for ER retention, likely within the ER lumen.
• These findings contribute to understanding HBV protein synthesis and intracellular trafficking.