5SrRNA

5S ribosomal RNA (5S rRNA) is a small, highly conserved non-coding RNA that forms an essential part of the large ribosomal subunit in all domains of life. In bacteria, archaea, and eukaryotes, 5S rRNA contributes to the structural framework of the 50S or 60S subunit and plays a role in ribosome assembly and function.

The mature molecule is about 120 nucleotides long and adopts a compact secondary structure with several helices forming a core. The sequence and structure are highly conserved, with characteristic motifs shared across domains. Its three-dimensional fold allows interactions with ribosomal proteins that help stabilize the large subunit and bridge to the small subunit during translation.

Genetically, 5S rRNA genes are organized differently among organisms. In bacteria, 5S rRNA is typically encoded in rrn operons together with 16S and 23S rRNA and transcribed by RNA polymerase I as part of a single transcript that is processed. In archaea and eukaryotes, separate 5S rRNA genes exist and are transcribed by RNA polymerase III in the nucleus, with multiple genomic copies to meet cellular demand. In some species, regulatory elements coordinate expression with ribosome biogenesis.

In function, 5S rRNA participates in maintaining the architecture of the large subunit, stabilizing inter-subunit contacts, and aiding proper placement of ribosomal proteins. It contributes to the structure near the central protuberance and participates in assembly of the ribosome, supporting accurate and efficient translation.

Evolutionarily, the 5S rRNA gene is highly conserved, making it useful in phylogenetic analyses. Its basic features are preserved, though copy number and genomic organization vary among organisms.