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A Viral Biorealm page on the genus Bromovirus

Electron Micrograph of a bromovirus by Thorben Lundsgaard, Dr C.J. Woolston and Ed Rybicki.

Baltimore Classification

Higher order taxa

Viruses; ssRNA positive-strand viruses, no DNA stage; Bromoviridae; Bromovirus


Broad bean mottle virus, Brome mosaic virus, Cassia yellow blotch virus, Cowpea chlorotic mottle virus, Spring beauty latent virus

Description and Significance

The genus Bromovirus is one of five genera in the Bromoviridae family. It has a tripartite genome and an encapsidated subgenomic RNA from which the coat protein is expressed.

Some members of the virus are transmitted by beetles while the virus is readily transmissible experimentally by mechanical inoculation. (source: Plant Viruses Online)

Genome Structure

The genome is segmented and tripartite. The segments are distributive among 3 particle types of different sizes. The genome consists of three to four segments of linear, positive-sense, single-stranded RNA. The virion may contain minor species of non-genomic nucleic acid. Although the encapsidated nucleic acid is mainly of genomic origin, the virions may also contain subgenomic RNA. Subgenomic RNA is the mRNA (RNA-4, a subgenomic fragment of RNA-3) derived from genomic RNA-3.

The complete genome is fully sequenced and is 8620-8800 nucleotides long. RNA-1 has been fully sequenced and 3158-3372-3900 nucleotides long; RNA-2 has been fully sequenced and 2799-3032-3400 nucleotides long; RNA-3 is sequenced but only an estimate is given and the sequence is 2117-2296-2600 nucleotides long; RNA-4 has been fully sequenced and is 800 nucleotides long.

The genome has a base ratio of 24.4-25.95-28 % guanine; 24.9-26.05-27 % adenine; 19-20.62-22.2 % cytosine; 24-27.42-29 % uracil. The genome has a guanine+cytosine content of 44-49 %.

The 5'-end of the genome has a methylated nucleotide cap and the cap sequence type is m7G5'ppp5. The 3'-terminus has on all genomic RNAs a tRNA-like structure that accepts tyrosine. The genome does not have a poly (A) region. The multipartite genome is divided among more than one type of particles and the segments are distributed between 3 different types of particles. The largest particles each contain one molecule of RNA-1; the medium sized particles each contain one molecule of RNA-2; and the smallest particles contain one molecule each of RNA-3 and RNA-4. (source: ICTV dB Descriptions)

Virion Structure of a Bromovirus

The virions of a bromovirus consist of a capsid that is not enveloped and round with icosahedral symmetry. The isometric capsid has a diameter of 25-26.16-28 nm. The capsids appear round. The capsomer arrangement is either clearly visible or not obvious. The capsid consists of 32 capsomers. (source: ICTV dB Descriptions)

Reproduction Cycle of a Bromovirus in a Host Cell

Viral Ecology & Pathology


Plant Viruses Online

ICTV dB Descriptions