Notes on Family: Bromoviridae

icosahedra or bacilliform
icosahedra or bacilliform
icosahedra or bacilliform

Contents

General Description

This family is characterised by its isometric or quasi-isometric particles and its single strand, positive-sense, RNA in three genomic and one subgenomic segments. These are packaged separately, resulting in several different types of virion, which may or may not differ in size (depending on the genus).

Morphology

Virions isometric to quasi-isometric, elongated, not enveloped, 26-35 nm in diameter. Symmetry icosahedral (T = 3, or T = 1 in Alfamovirus Ta particle). Surface projections of nucleocapsid not present. Shell of virion has a single layer.

Particles contain 14-25 % nucleic acid.

Genomen

Positive sense single-stranded RNA. There are three genomic RNAs (RNA1, 3200-3644 nt; RNA2, 2600-3050 nt; RNA3, 2100-2216 nt) and one encapsidated subgenomic derived from RNA3 (800-1000 nt) from which the coat protein is expressed. Total genome 7900-8910 nucleotides long. 3'-terminal sequences are conserved. The 5' terminus of each RNA has a methylated nucleotide cap with the sequence: m7G5'ppp5'Gp....

Genera in the Family

  • Alfamovirus (bacilliform virions of several size; 3 major species of RNA)
  • Anulavirus (quasispherical virions 25-35 nm in diamter; RNA2 smaller than RNA3)
  • Bromovirus (icosahedral virions, 26 nm in diameter)
  • Cucumovirus (icosahedral virions, 29 nm in diameter)
  • Ilarvirus (icosahedral virions of three sizes, 26-35 nm in diameter)
  • Oleavirus (bacilliform virions of several sizes; 4 major species of RNA; not transmitted by aphids)