Papers in the Biological Sciences



Feng Qu

Date of this Version



Published in Encyclopedia of Virology, 2nd edition, ed. R.G. Webster & A. Granoff, Academic Press, 1999, pp. 243-247.


Copyright © 1999 Academic Press. Used by permission.


Carmovirus is one of two officially recognized genera of Tombusviridae. Members of Tombusviridae all have icosahedral virions of about 30 nm in diameter with T = 3 symmetry that consists of 180 coat protein (CP) subunits of about 38- 43 kDa and a single-stranded (ss) RNA genome ranging in size from 4.0 to 4.7 kb. Carmoviruses share recognizable sequence similarity in both the polymerase and structural genes with members of the other genus, Tombusvirus. Sequence comparisons and phylogenetic analysis of these genes support the view that the genera are distinct but closely related. In addition, the genome organization of the carmoviruses is characteristically different from that of the tombusviruses.

Carmoviruses contain a single-component positive-sense genome of about 4.0 kb. The genome, as exemplified by turnip crinkle virus (TCV) in Figure 1, consists of five open reading frames (ORFs) which encode proteins of about 28, 88, 8, 9 and 38 kDa from the 5’ to the 3’ end, respectively. The virions are icosahedral and consist of 180 CP subunits of approximately 38 kDa. The genus name is derived from the first member of the genus to be sequenced, carnation mottle virus (CarMV). Much more detailed knowledge about virus structure and genome function is, however, known for TCV because its crystal structure has been determined and it was the first carmovirus for which infectious transcripts were produced from a cDNA clone of the genome. To date, the nucleotide sequences of six definitive carmoviruses have been determined (Table 1). These sequenced members share similar morphological and physicochemical properties with about 20 other viruses listed in Table 1 that are recognized as species or tentative species, depending on the characterized molecular detail of the viruses. Unlike the majority of tombusviruses, carmoviruses are sufficiently distant from each other to prevent them cross reacting in standard RNA hybridization or serological tests.