Brome mosaic virus, good for an RNA virologistís
C. Cheng Kao and K. Sivakumaran
Department of Biology, Indiana University, Bloomington, IN 47405, USA
||Type member of the Bromovirus
genus, family Bromoviridae. A member of the alphavirus-like
supergroup of positive-sense single-stranded RNA viruses.
||Virions are nonenveloped
icosahedrals made up of 180 coat protein subunits (Fig. 1). The particles
are 26 nm in diameter and contain 22% nucleic acid and 78% protein. The
BMV genome is composed of three positive-sense, capped RNAs: RNA1 (3.2
kb), RNA2 (2.9 kb), RNA3 (2.1 kb) (Fig. 2).
||RNA1 encodes protein 1a, containing
capping and putative RNA helicase activities. RNA2 encodes protein 2a, a
putative RNA-dependent RNA polymerase. RNA3 codes for two proteins: 3a,
which is required for cell-to-cell movement, and the capsid protein. The
capsid is translated from a subgenomic RNA, RNA4 (1.2 kb).
||Monocots in the Poacea family,
including Bromus inermis, Zea mays and Hordeum vulgare, in which BMV
causes brown streaks. BMV can also infect the dicots Nicotiana benthamiana
and several Chenopodium species. In N. benthamiana, the infection is
asymptomatic while infection of Chenopodium can cause either necrotic or
micrograph of brome mosaic virus. The average diameter of each particle is
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