From: Small RNA modifications: regulatory molecules and potential applications
Classification | Length (nt) | Precursor | Processing | Function | References |
---|---|---|---|---|---|
Micro RNA(miRNA) |  ~ 20–25 | Hairpin loop-like precursor miRNA | transcribed by RNA pol II, cleaved by Drosha/DGCR8 and Dicer | Binds to Argonaute protein and forms a RISC complex that participates in transcriptional gene silencing, inhibition of mRNA translation and in mRNA decay | |
PIWI-interacting RNA(piRNA) |  ~ 18–30 | Long single-stranded RNA | transcribed by RNA pol II, processing by primary procession pathway and ping-pong cycle by Zuc, Aub, AGO3 | Interacts with PIWI proteins to regulate gene silencing in a miRNA-like manner and regulates germ cell genome stability through recruitment of epigenetic regulators | |
Small interfering RNA(siRNA) |  ~ 20–25 | Long double-stranded RNA | transcribed by RNA pol II, processing by Dicer to cleavage | Binds to Argonaute protein and forms a RISC complex that participates in mediating mRNA decay | |
Transfer RNA(tRNA) |  ~ 74–93 | Precursor tRNA | transcribed by RNA pol III, processing by Ribonuclease P, Ribonuclease Z,endonuclease nucleotidyl transferase to cleavage and modify | Transports amino acids to the ribosome to synthesize polypeptide chains | |
Small nuclear RNA (snRNA) |  ~ 90–200 | \ | Transcripted by RNA polymerase III and II | Combines with proteins to form small nuclear ribonucleoproteins (snRNPs) involved in pre-mRNA splicing | [23] |
Small nucleolar RNA (snoRNA) |  ~ 60–400 | \ | Transcribed by RNA polymerase II, processing by ribonuclease | Binds to specific proteins to form small nucleolar ribonucleoprotein (snoRNPs) that regulate the modification of ribosomal RNA (rRNA) | [24] |
5S RNA | 120 | pre-5S RNA | Transcribed by RNA polymerase III | Binds to ribosomal protein L5 to form a stable complex that is involved in the assembly of the larger ribosomal subunits | [25] |
Vault RNA (vtRNA) |  ~ 88–140 | \ | Transcribed by RNA polymerase III | Binds to Vault proteins and form complexes; functions remain poorly characterized | |
Y RNA |  ~ 80–110 | \ | Transcribed by RNA polymerase III, processing by ribonuclease | Binds to Ro60 protein and La protein to form Ro-RNP (Ro60 containing ribonucleoprotein) complex which regulates RNA stability, cellular stress responses, as well as initiation of chromosomal DNA replication and Ro60 protein activation | |
Transfer RNA-derived small RNA (tsRNA) |  ~ 15–40 | tRNA | Cleaved by Angiogenin, Dicer, RNase T2, RNase Z, ELAC2, Rnylp, etc | Functions by mimicry or displacement of tRNA; forms RNP complexes; binds to Argonaute | |
Y RNA derived small RNA (ysRNA) |  ~ 22–25 and ~ 27–36 | Y RNA | May cleaved by Caspase or RNsase1 | Function is unclear; abundant in extracellular spaces, such as in serum, plasma and other biofluids | |
vtRNA derived small RNA (vtsRNA) |  ~ 23–32 | vtRNA | Dicer | Function is unclear; predicted to function in a miRNA-like manner | |
ribosomal RNA derived small RNA (rsRNA) |  ~ 21–44 | rRNA | Unclear | Function is unclear; enriched in mature mouse sperm; present in human peripheral blood serum; its presence is linked with inflammation in humans | |
Small nucleolar RNA derived small RNA (snosRNA) | 17–19; 20–24; > 26 | snoRNA | Unclear | Function is unknown; likely resembles miRNA; can associate with argonaute proteins and influence translation; longer snosRNAs may form complexes with hnRNPs and influence gene expression |