Higher order taxa
Viruses; Retro-transcribing viruses; Reoviridae
Alpharetrovirus, Betaretrovirus, Spumavirus (examples)
Description and Significance
The genome of retroviridae is dimeric, unsegmented and contains a single molecule of linear. The genome is -RT and a positive-sense, single-stranded RNA. Minor species of non-genomic nucleic acid are also found in virions. The encapsidated nucleic acid is mainly of genomic origin but virions may also contain nucleic acid of host origin, including host RNA and fragments of host DNA believed to be incidental inclusions. The complete genome of one monomer is 700-11000 nucleotides long. The 5'-end of the genome has a methylated nucleotide cap with a cap sequence type 1 m7G5ppp5'GmpNp. The 3'-terminus of each monomer has a poly (A) tract and the terminus has a tRNA-like structure. (source: ICTVdB Descriptions)
Virion Structure of a Retroviridae
The virions of a retroviridae consist of an encelope, a nucleocapsid and a nucleoid. The virus capsid is enveloped. The virions are spherical to pleomorphic and measure 80-100 nm in diameter. The surface projections are small or distinctive glycoprotein spikes that cover the surface evenly. The projections are densely dispersed and 8 nm long. The nucleoid is concentric or eccentric while the core is spherical.