rRNAgenen

Ribosomal RNA genes, often referred to as rRNA genes, encode the RNA components of ribosomes, the cellular machines that translate messenger RNA into proteins. rRNA genes are highly conserved across life and typically exist in many copies, reflecting their essential role in protein synthesis.

In bacteria and archaea, rRNA genes are usually arranged in operons containing the 16S, 23S, and 5S rRNA genes in that order. These operons can be present in multiple copies throughout the genome and are transcribed as a single precursor by RNA polymerase. The precursor is processed to yield mature 16S, 23S, and 5S rRNAs that form parts of the small and large ribosomal subunits.

In eukaryotes, rRNA genes are found in tandem repeats within nucleolar organizer regions on several chromosomes. The primary transcript, called the 45S pre-rRNA, encodes the 18S, 5.8S, and 28S rRNAs and is transcribed by RNA polymerase I. The separate 5S rRNA gene is transcribed by RNA polymerase III. These transcripts are processed and assembled with ribosomal proteins to form the small (40S/18S) and large (60S/28S-5.8S) ribosomal subunits. In humans, hundreds of rDNA repeats exist per genome.

Functionally, rRNA molecules form the core structural and catalytic components of ribosomes, providing scaffolding for ribosomal proteins and participating in the peptidyl transferase activity and decoding of mRNA.

rRNA genes are highly conserved but exhibit lineage-specific variations. In bacteria, 16S rRNA gene sequences are commonly used for phylogenetic analysis and taxonomy. Copy number, sequence variation, and concerted evolution of rRNA gene repeats can influence their evolution and interpretation.

Applications include microbial identification, environmental sequencing, and diagnostic assays such as qPCR and barcode sequencing.