VIRION
Non-enveloped, rod of filaments of 7nm in diameter and 700 to 2000nm in length. Helical capsid with adsorption proteins on one end.
GENOME
Circular, ssDNA genome (+) of 4.5 to 8kb encoding for 4 to 10 proteins. Replication occurs via dsDNA intermediate and rolling circle.
GENE EXPRESSION
Each gene is transcribed by host cellular machinery, via a specific promoter. Some genes end by a transcription terminator.
ENZYMES
REPLICATION
CYTOPLASMIC
- Viral g3p protein mediates pilus-mediated adsorption of the virus onto host cell. Pilus retraction pulls the virion to the host internal membrane.
- The proteins of the capsid perform the injection of the viral DNA through bacterial membranes into cell cytoplasm.
- Host polymerase convert the (+)ssDNA viral genome into a covalently closed dsDNA called replicative form DNA (RF).
- dsDNA transcription by host RNA polymerase gives rise to viral mRNAs.
- Viral g2p protein nicks RF DNA strand at the origin of replication.
- (+) strand replication occurs by rolling circle.
- New (+)ssDNA genomes are converted into new RF molecules, and further transcription occurs.
- When enough g5p protein is synthesized, conversion into RF dsDNA is inhibited, as neo-synthesized genomic ssDNA is covered with g5p.
- g5p are replaced by g8p proteins to trigger the assembly of the viral capsid.
- New virions are secreted from host cell.
- Infected cells continue to divide and produce virions indefinitely.
