Table 1.

The world of ncRNAs. ncRNAs discussed in this review, organized by approximate size ranges in nucleotides. (The full list of ncRNAs includes ultra-short RNAs (less than 18 nt), satellite-associated RNAs, promoter-associated RNAs, half tRNAs and others.)

18–24	miRNAs; endo-siRNAs
18–40	small RNAs processed from abundant cellular ncRNAs; small RNAs processed from TE transcripts
25–30	small RNAs processed from abundant cellular ncRNAs (pincRNAs) that are specifically regulated by learning
25–35	typical piRNAs expressed in the germline (and in somatic tissues at lower levels)
70–110	pre-miRNAs (miRNA small hairpin precursors)
70–300	abundant cellular ncRNAs: tRNAs, snoRNAs, Y RNAs, vault RNAs, snRNAs and 5S rRNA
100–300	Alu-related RNA transcripts; BC1; BC200
>300	long intronic and intergenic ncRNAs, pri-miRs (primary miRNA gene transcripts), antisense RNAs, circular RNAs, TE transcripts, 18S and 28S ribosomal RNAs