Ribosomal RNA

Definition

The catalytic RNA component of ribosomes that translates messenger RNA into proteins; the most abundant cellular RNA and a ribozyme that directly catalyzes peptide-bond formation. In arthropod systematics, specific rRNA subunits—particularly 18S (small subunit) and 28S (large subunit) rRNA—serve as conserved molecular markers for reconstructing deep phylogenetic relationships among insects, arachnids, and crustaceans due to their universal presence, slow evolutionary rate, and mosaic of conserved and variable regions.

Etymology

From ribosome + -al + RNA (ribonucleic acid), 1960s

Example

Comparative sequencing of 18S rRNA helped resolve the controversial placement of Hexapoda within Pancrustacea, revealing closer evolutionary ties between insects and certain crustacean groups than previously recognized by morphology alone.

Synonyms

• rRNA

Related Terms

• Ribosome
• transfer RNA
• messenger RNA
• ribosomal DNA
• molecular systematics
• Phylogenetics
• 18S rRNA
• 28S rRNA
• ribozyme

Usage Notes

Distinguish rRNA (the functional RNA molecule) from rDNA (the genes encoding it). In practice, 'rRNA' often refers to the gene or sequence data rather than the cellular molecule. The 16S rRNA of prokaryotes and mitochondria is analogous to 18S rRNA in eukaryotes; mitochondrial 12S and 16S rRNA are frequently used in insect and arachnid phylogeography. rRNA sequences are preferred for deep phylogeny but may saturate at shallow divergences; protein-coding genes often supplement them for recent divergences.