23S

23S refers to the 23S ribosomal RNA, a component of the prokaryotic large ribosomal subunit. In bacteria and archaea, it is part of the 50S subunit and is encoded by rrl (or equivalent) within rRNA operons that typically also include the 16S and 5S rRNA genes. The mature 23S rRNA in bacteria is about 2,900 nucleotides long, though length varies among species. The equivalent in eukaryotes is the 28S rRNA, while mitochondria and chloroplasts retain organellar homologs.

Functionally, 23S rRNA contributes to the peptidyl transferase center, catalyzing peptide bond formation during protein synthesis. Its three-dimensional structure consists of multiple domains, with domain V housing the active site and interacting with many ribosomal proteins that form the catalytic center and the polypeptide exit tunnel of the ribosome. This rRNA is highly conserved across bacteria and archaea, reflecting its essential role in translation.

Genetically, in bacteria the transcription of the rRNA operon yields a single precursor that is processed into the mature 16S, 23S, and 5S rRNAs. The copy number of rrn operons varies among species and can influence growth rate and protein production, with some bacteria possessing multiple operons to meet metabolic demand.

Evolutionarily, the 23S rRNA gene is widely used in phylogenetic analyses and taxonomy of prokaryotes. Its sequence is highly conserved, yet contains variable regions that enable discrimination at various taxonomic levels. In combination with 16S and 5S data, 23S rRNA contributes to resolving evolutionary relationships among bacteria and archaea.

Clinically, the 23S rRNA forms part of binding sites for several antibiotics targeting the 50S subunit, including chloramphenicol and macrolides. Resistance can arise through mutations in the 23S rRNA gene or by methylation of specific residues, reducing drug binding and efficacy.