VIRION
Non-enveloped, round, T=1 icosahedral symmetry, 21-22 nm in diameter. The capsid consists of 60 copies of CP protein VP1.
GENOME
Linear, ssDNA genome of about 6kb in size, with long inverted terminal repeats (550 nt). Equal amount of positive and negative strands are encapsidated, although the percentage of particles encapsidating the positive strand can be lower depending on the host cell. ORFs for the structural and non-structural proteins are located on both DNA strands.
The genome is replicated through rolling-hairpin mechanism.
GENE EXPRESSION
Host proteins transcribe the genomes into mRNAs.
Alternative mRNAs splicing and leaky scanning allow expression of NS and VP products. The structural and non-structural transcripts overlap for 60 nt at the 3? ends (antisense RNAs).
VP1 capsid protein displays phospholipase A2 activity.
ENZYMES
REPLICATION
NUCLEAR
- Attachement to host receptors initiates clathrin-mediated endocytosis of the virion into the host cell.
- The virion penetrates into the cytoplasm via permeabilization of host endosomal membrane.
- Microtubular transport of the virion toward the nucleus.
- The viral ssDNA genome penetrates into the nucleus.
- The ssDNA is converted into dsDNA by cellular proteins.
- dsDNA transcription gives rise to viral mRNAs when host cell enters S phase and translated to produce viral proteins.
- Replication occurs through rolling-hairpin mechanism, with NS1 endonuclease binding covalently to the 5' genomic end.
- Individual ssDNA genomes are excised from replication concatemers by a process called junction resolution.
- These newly synthesized ssDNA can either
a) be converted to dsDNA and serve as a template for transcription/replication
b) be encapsidated to form new virions that are released by cell lysis.
