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Joined 2026-09-21 Message
Incoming links: Phylogenetic analysis
16S ribosomal RNA 2026-11-05
16S ribosomal RNA is the ribosomal RNA of the small ribosomal subunit in bacteria and archaea. Together with ribosomal proteins, this RNA forms the small subunit's architecture, which positions messenger RNA for translation. The name refers to a sedimentation coefficient of about16 svedbergs: it is neither a count of subunits nor a length in nucleotides. The RNA molecule and the DNA gene encoding it are different molecules, even when a DNA sequencing assay is informally described as “16S sequencing”.[ref]
Structure of the 30S ribosomal subunit by B. T. Wimberly and others. Abstract: bacterial30S structure and its RNA–protein architecture
A structural example is the bacterial30S small ribosomal subunit: the2000 X-ray crystallography study of B. T. Wimberly and colleagues resolved its RNA–protein architecture at3Å resolution. At a different scale, 16S ribosomal RNA sequences can serve as inherited characters for phylogenetic analysis. The1977 study by George E. Fox and colleagues compared ribosomal RNA oligonucleotide cataloguing results from methane-producing organisms with those from other organisms, helping expose a deep evolutionary division.[ref][ref]
Classification of methanogenic bacteria by 16S ribosomal RNA characterization by George E. Fox and others. Abstract and pp.4537–4541: comparative16S characterization
A useful caution is that one genome need not contain just one16S gene, and its copies need not have identical nucleotide sequences. Silvia G. Acinas and colleagues explicitly measured this variation across sequenced genomes. As a hypothetical example, two distinct16S DNA sequences recovered from a sample could represent two organisms, or two copies in one organism. Counting distinct sequences therefore requires more interpretation than counting organisms.[ref]
Divergence and redundancy of 16S rRNA sequences in genomes with multiple rrn operons by Silvia G. Acinas and others. Abstract: intragenomic variation and copy-number effects
Orthoretrovirinae 2026-11-05
Orthoretrovirinae is the subfamily of Retroviridae containing Lentivirus and several other retroviral genera. It includes human immunodeficiency virus and feline immunodeficiency virus. The family placement describes a replication strategy; it does not imply one host range or one disease outcome for all members.[ref]
Orthoretrovirinae report by the International Committee on Taxonomy of Viruses. Subfamily classification and Distinguishing features
A typical virion packages two copies of its RNA genome. After entry and release of the viral core into a host cell, reverse transcription produces DNA that can become an integrated provirus. Proteolytic processing of a viral polyprotein also releases functional components during maturation.[ref]
Orthoretrovirinae report by the International Committee on Taxonomy of Viruses. Distinguishing features, RNA copies, reverse-transcription timing and protease processing
[ref]Retroviridae report by the International Committee on Taxonomy of Viruses. Table 1, replication and integration
An invented counting example clarifies the two-copy description. If each packaged RNA molecule has 10,000 nucleotides, the pair contains 20,000 RNA nucleotides in total. The length of one genome copy is still 10,000 nucleotides. A corresponding 10,000-base-pair double-stranded DNA molecule contains 20,000 DNA nucleotides, but its length is conventionally reported in base pairs. Copy count, nucleotide count and base-pair length answer different questions.
The subfamily's genera are distinguished in part by phylogenetic analysis of conserved reverse-transcriptase regions. A shared enzyme mechanism can coexist with differences in accessory proteins, host distribution and cellular targets. Observing the shared mechanism therefore provides a classification clue while leaving those other biological properties to be determined.[ref]
Orthoretrovirinae report by the International Committee on Taxonomy of Viruses. Genus demarcation criteria and differences among members
Spumaretrovirinae 2026-11-05
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.[ref]
Retroviridae report by the International Committee on Taxonomy of Viruses. Derivation of names, Spumaretrovirinae; Relationships within the family
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.[ref]
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
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.[ref]
Spumaretrovirinae report by the International Committee on Taxonomy of Viruses. Distinguishing features, assembly, typical genome and Pro/Pol expression
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.