HBV Flashcards
What family is HBV in?
What genus is HBV in?
Family - hepadnaviridae
Genus - Orthohepadnavirus
Which 3 HBV particles are there?
22nm HBsAg
45nm Dane Particle
Pleiomorphic HBsAg filaments
Describe the HBV genome
- relaxed circular DNA (rcDNA)
3. 2kb partially double stranded.
How is the circularity maintained?
Overlapping 5’ ends
Which strand in HBV is longer? The positive or negative strand?
Negative strand
What is required for attachment and entry of HBV?
L surface antigen.
Unknown receptor.
How is HBV taken up?
Endocytosis, membrane fusion occurs between viral and cellular membrane.
How does rcDNA convert to cccDNA?
P protein is removed
Both strands are completed and ligated by host cellular enzymes in the nucleus
What is the template for transcription for HBV?
cccDNA
What is the role of HBV X protein?
Transcriptional activator
Doesnt bind DNA itself, activates transcription factors and interacts with cell signalling papthways
What does nuclear export of mRNAs into the cytoplasm depend on?
Post transcriptional regulatory element - PRE. that uses the Crm1/RAN-GTP pathway but no viral protein is required.
There are 4 different mRNAs made in transcription in HBV. How long is each one and what does it encode?
- 5kb - pregenomic RNA, C and P protein
- 4kb - L form of the S antigen
- 1kb - M and S form of the S antigen
- 7kb - encodes X protein
How is the 3.5kb mRNA translated?
Leaky scanning.
How is the 2.1kb mRNA translated?
It has 2 promoters very close together. The 1st encodes the M antigen and the 2nd initates txn just downstream of the start site.
What is the signal for core particle assembly in HBV?
P:RNA complex
Compare the HIV and HBV reverse transcriptases
Both have polymerase and RNase H domain
HBV p protein has a spacer and terminal protein (larger N term domain)
Tyrosine 96 is the primer for -sense DNA strand synthesis whereas the HIV RT uses tRNA as a primer.
What determined the fate of core particles in HBV?
Concentration of L surface antigen.
What does low concentration of L lead to?
Core particle enters the nucleus and is converted to cccDNA
What does a high concentration of L lead to?
Core particle buds into the ER. Virions exit the cell by exocytosis.
What happens to empty HBsAg particles?
Bud into the ER and undergo exocytosis.
