Non-enveloped, round, T=1 icosahedral symmetry, about 18-19 nm in diameter.
Multipartite ssDNA genome (+) composed of 6 to 8 circular segments about 1kb in size. Each ssDNA segment have a common stem-loop region and are encapsidated in a separate particle.
In addition to genomic DNA, up to 4 satellite-like DNAs are found in some isolates, usually encoding for accessory Rep proteins (para-Rep). These satellite-rep proteins are only able to initiate replication of their genomic DNA, unlike genomic encoded Master-Rep (M-Rep) which promotes replication of all 6 viral genomic ssDNAs (trans-replication).
Each ssDNA genome segment is monocistronic, except for BBTV DNA-R which contains a second small ORF U5 internal to the Rep-encoding ORF. U3 and U5 are absent in ABTV.
- Virus penetrates into the host cell.
- Uncoating, the viral ssDNA genome penetrates into the nucleus.
- The ssDNA is converted into dsDNA with the participation of cellular factors.
- Bidirectional dsDNA transcription from the IR promoter produces viral mRNAs and translation of viral proteins.
- Replication is initiated by cleavage of the (+)strand by REP, and occurs by rolling circle producing ssDNA genomes.
- These newly synthesized ssDNA can either
a) be converted to dsDNA and serve as a template for transcription/replication
b) be encapsidated by CP and form virions that will be released in the extracellular space. c) be transported outside the nucleus, to a neighboring cell through plasmodesmata (cell-cell movement) with the help of viral movement proteins.