Table 1.

Different types of noncoding RNAs

Noncoding RNA	Function
Ribosomal RNA (rRNA)^a	RNA components of ribosome, large and small subunits
Transfer RNA (tRNA)^a	Amino acid transfer during translation elongation
Small nuclear RNA (snRNA)^a	Nuclear RNA processing, including splicing
Small nucleolar RNA^a	Direct necessary chemical modifications of rRNAs, also tRNAs and snRNAs
microRNA^b	18- to 24-nt posttranscriptional regulators of mRNA translation; known regulatory roles in developmental timing
Piwi-interacting RNA^b	Testis-specific, 25- to 32-nt small RNA; ~30% are associated with repeat/transposon sequences; regulatory role in controlling transposition
Endogenous small interfering RNA^b	21-nt small RNA derived from long double-strand RNA; regulate transcript stability through the RNA interference pathway, also associated with repeat/transposon sequences
Y RNA^a	RNA component of Ro ribonucleoprotein complexes involved in 5S rRNA quality control; also implicated in DNA replication
SRP RNA^a	RNA component of the signal recognition particle (SRP) required for cotranslational targeting of proteins to membranes
Long noncoding RNA^b	Generally noncoding RNAs ≥200 nt, including Xist, TSIX, AIR, HOTAIR, H19 Evf, and others. Commonly associated with imprinted regions and DNA methylation and may have regulatory function in establishing or maintaining chromatin structure

Housekeeping.

Regulatory.