Medicine & USMLE

Small Nuclear RNA (snRNA)

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RNA
  1. Messenger RNA (mRNA)
  2. Ribosomal RNA (rRNA)
  3. Transfer RNA (tRNA)
  4. Small Nuclear RNA (snRNA)
  5. MicroRNA (miRNA)
  6. Small Interfering RNA (siRNA)

Summary

Small nuclear RNA, or snRNA, is a class of non-coding RNA responsible for processing of mRNA. snRNA combines with various proteins to form small nuclear ribonucleoproteins or snurps, which then combine with other proteins and mRNA to form spliceosomes. These spliceosomes cut out non-coding sequences in mRNA, joining together the remaining coding sequences to form mature mRNA. snRNA is synthesized mainly by RNA polymerase II in the nucleus of eukaryotes, and is not found in prokaryotes.

Key Points

  • Small Nuclear RNA (snRNA)
    • Naming
      • Small RNA molecules that are found within the nucleus
    • Characteristics
      • Class of non-coding RNA
        • Does not code for proteins
        • Also known as functional RNA
      • Found in eukaryotes
    • Function
      • Combine with various proteins to form small nuclear ribonucleoproteins (snRNPs), which assist in splicing pre-mRNA strands in the nucleus
        • Maturation of an mRNA strand includes splicing of the transcript to remove introns (noncoding sequences) and join the flanking exons (coding sequences) together
        • Splicing is accomplished by snRNPs and other associated proteins coming together and forming a spliceosome
          • Spliceosomes recognize both the 5’ and 3’ splice sites of introns, pinch them off, and ligate the remaining exons to form mature mRNA
            • The splice sites are also known as the 5’-splice donor site and 3’-splice acceptor site
    • Synthesis
      • Transcribed mostly by RNA Polymerase II 
        • Some are transcribed by RNA Polymerase III
        • Occurs in the nucleus