= Spumaretrovirinae
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<Spumaretrovirinae> is a subfamily of <Retroviridae> that includes the foamy <viruses>. The name refers to a characteristic foamy appearance that many isolates produce in <cell culture>. That visible effect is one observation within a classification also supported by molecular features and <phylogenetic analysis>.<Retroviridae report by the International Committee on Taxonomy of Viruses>[Derivation of names, Spumaretrovirinae; Relationships within the family]{ref}
A notable feature concerns the timing of <reverse transcription>. Released <virions> can already contain substantial reverse-transcribed <DNA>. In <Orthoretrovirinae>, the usual packaged <genome> is instead two <RNA> copies and <reverse transcription> follows entry into a new host <cell>. Both groups use a <DNA> stage in their replication cycles.<Spumaretrovirinae report by the International Committee on Taxonomy of Viruses>[Distinguishing features, reverse-transcribed DNA in virions]{ref}<Orthoretrovirinae report by the International Committee on Taxonomy of Viruses>[Distinguishing features, RNA packaging and post-entry reverse transcription]{ref}
The ICTV account also describes cytoplasmic <capsid> assembly and a <genome> of roughly 11.6 kilobases for a typical spumavirus. Its viral enzyme precursor is expressed from a spliced transcript, rather than the same fused precursor arrangement emphasized for <Orthoretrovirinae>.<Spumaretrovirinae report by the International Committee on Taxonomy of Viruses>[Distinguishing features, assembly, typical genome and Pro/Pol expression]{ref}
The timing distinction gives a useful experimental question: at which point in the cycle is a particular nucleic-acid form present? Detecting <DNA> in released particles and detecting newly made <DNA> after entry describe different stages. A single positive measurement, without identifying the sampled stage and material, cannot reconstruct when conversion occurred. Molecular form, location and sequence in time are complementary evidence.
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