Description of Retroviridae

adapted from ICTVdb

Virion Properties

Morphology

Virions consist of an envelope, a nucleocapsid, and a nucleoid. Virus capsid is enveloped. Virions are spherical to pleomorphic. Virions measure 80-100 nm in diameter. Surface projections are densely dispersed, small or distinctive glycoprotein spikes that cover evenly the surface. Surface projections are 8 nm long. The nucleoid is concentric, or eccentric. The core is spherical.

Only one species is recovered in preparations.

Physicochemical and Physical Properties

Virions have a buoyant density in sucrose of 1.13-1.18 g cm^-3.

Nucleic Acid

The Mr of the genome constitutes 2% of the virion by weight. The genome is dimeric (monomers held together by hydrogen bonds, not segmented and contains a single molecule of linear.

Description of Retroviridae

adapted from ICTVdb

Virion Properties

Morphology

Virions consist of an envelope, a nucleocapsid, and a nucleoid. Virus capsid is enveloped. Virions are spherical to pleomorphic. Virions measure 80-100 nm in diameter. Surface projections are densely dispersed, small or distinctive glycoprotein spikes that cover evenly the surface. Surface projections are 8 nm long. The nucleoid is concentric, or eccentric. The core is spherical.

Only one species is recovered in preparations.

Physicochemical and Physical Properties

Virions have a buoyant density in sucrose of 1.13-1.18 g cm^-3.

Nucleic Acid

The Mr of the genome constitutes 2% of the virion by weight. The genome is dimeric (monomers held together by hydrogen bonds, not segmented and contains a single molecule of linear. The genome is -RT. The genome is 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 is of one monomer 7000-11000 nucleotides long. The 5'-end of the genome has a methylated nucleotide cap; cap sequence type is of type 1 m7G5ppp5'GmpNp. The 3'-terminus has of each monomer a poly (A) tract. The 3'-terminus has a tRNA-like structure.

Proteins

Proteins constitute about 60% of the particle weight.

The viral genome encodes structural proteins and non-structural proteins.

Non-Structural Proteins: The virus codes for an RNA-dependent DNA polymerase.

Lipids

Lipids are present and located in the envelope. Virions are composed of 35% lipids by weight. The composition of viral lipids and host cell membranes are similar. The lipids are of host origin and are derived from plasma membranes.

Polyamines

Other compounds that have been detected in the virus particles are 3% carbohydrates.

Genome Organization and Replication

By itself, genomic nucleic acid is not infectious (when purified).

Translation: Replication involves a reverse transcription step.