Topocuvirus (taxid:220339)



Non-enveloped, about 38 nm in length and 22 nm in diameter (for MSV), twinned (geminate) incomplete T=1 icosahedral symmetry capsid that contains 22 pentameric capsomers made of 110 capsid proteins (CP). Each geminate particle contains only a single circular ssDNA.



Monopartite, circular, ssDNA genome (+) genome of 2.86 kb. 3' terminus has no poly(A) tract. There are coding regions in both the virion (positive) and complementary (negative) sense strands.
The genome is replicated through double-stranded intermediates. The replication (Rep) protein initiates and terminates rolling circle replication, the host DNA polymerase being used for DNA replication itself. There is a potential stem-loop structure in the intergenic region that includes a conserved nonanucleotide sequence (TAATATTAC) where ssDNA synthesis is initiated.


Transcription is bidirectional from the common region (CR), which corresponds to the non-coding region common for topocu- and begomoviruses. 6 proteins are produced. In the V-sense: V2 and CP. In the C-sense: Rep, C2, C3 and C4.




  1. Virus penetrates into the host cell.
  2. Uncoating, the viral ssDNA genome penetrates into the nucleus.
  3. The ssDNA is converted into dsDNA with the participation of cellular factors.
  4. bidirectional dsDNA transcription from the IR promoter produces viral mRNAs and translation of viral proteins.
  5. Replication is initiated by cleavage of the (+)strand by REP, and occurs by rolling circle producing ssDNA genomes.
  6. These newly synthesized ssDNA can either
    a) be converted to dsDNA and serve as a template for transcription/replication
    b) be encapsidated by capsid protein and form virions released by cell lysis
    c) be transported outside the nucleus, to a neighboring cell through plasmodesmata (cell-cell movement) with the help of viral movement proteins.

Host-virus interaction

Cell-cycle modulation

Topocuvirus protein Rep is probably responsible for inhibiting host retinoblastoma protein and inducing transition from the G1 to S phase in preparation for virus replication since the virus targets differentiated non-dividing cells. .

Matching UniProtKB/Swiss-Prot entries

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6 entries grouped by protein

1 entry

Protein C4 (Protein L4)

Tomato pseudo-curly top virus (TPCTV) reference strain

1 entry

Protein C2 (Protein L2)

Tomato pseudo-curly top virus (TPCTV) reference strain

1 entry

Capsid protein (Coat protein) (CP)

Tomato pseudo-curly top virus (TPCTV) reference strain

1 entry

Putative movement protein (MP)

Tomato pseudo-curly top virus (TPCTV) reference strain

1 entry

Replication enhancer protein (REn) (16.1 kDa protein) (Protein C3) (Protein L3)

Tomato pseudo-curly top virus (TPCTV) reference strain

1 entry

Replication-associated protein (Rep) (EC 2.7.7.-) (EC 3.1.21.-) (Protein C1)

Tomato pseudo-curly top virus (TPCTV) reference strain