Table 2.
Classes of RNAs and their localization, size and function
| Class | Localization | Transcribed by | Function | Size | Disease |
|---|---|---|---|---|---|
| Messenger RNA (mRNA) | Nucleus and cytoplasm | Pol II | Gene expression into protein | 2–5 kb | na |
| Ribosomal RNA (rRNA) | Cytoplasm | Pol I | Translation, is part of the small or large subunit of the ribosome | 70S (prokaryotic) or 80S (eukaryotic) | Unknown |
| Micro RNA (miRNA) | Nucleus and cytoplasm | Pol II or Pol III | Inhibition of translation or degradation of mRNA | 21–23 bp | AD, PD, HD |
| Transfer RNA (tRNA) | Cytoplasm | Pol II or Pol III | Translation, brings cognate amino acid of mRNA to nascent polypeptide chain | 70–90 bp | PHC-2, PHC-4, neurodevelopmental and neurological disease |
| Long non-coding RNA (lncRNA) | Nucleus and cytoplasm | Pol II or Pol III | Diverse regulatory roles of other RNAs and proteins, chromatin remodeling | >200 bp | AD, SCA7 |
| Small nuclear RNA (snRNA) | Nucleus | Pol II or Pol III | Splicing of pre-mRNA | 100–300 bp | SMA |
AD Alzheimer’s disease, PD Parkinson’s disease, HD Huntington’s disease, PHC pontocerebellar hypoplasia, SCA spinocerebellar ataxia, SMA spinal muscular atrophy, na not applicable