Editing Gene expression (section)

===Non-coding RNA maturation===
{{main|TRNA#tRNA biogenesis|l1=tRNA maturation|RRNA#Prokaryotes vs. Eukaryotes|l2=rRNA maturation|MicroRNA#Biogenesis|l3=miRNA maturation}}
In most organisms [[ncRNA|non-coding genes (ncRNA)]] are transcribed as precursors that undergo further processing. In the case of ribosomal RNAs (rRNA), they are often transcribed as a pre-rRNA that contains one or more rRNAs. The pre-rRNA is cleaved and modified ([[2′-O-methylation|2′-''O''-methylation]] and [[pseudouridine]] formation) at specific sites by approximately 150 different small nucleolus-restricted RNA species, called snoRNAs. SnoRNAs associate with proteins, forming snoRNPs. While snoRNA part basepair with the target RNA and thus position the modification at a precise site, the protein part performs the catalytical reaction. In eukaryotes, in particular a snoRNP called RNase, MRP cleaves the [[45S pre-rRNA]] into the [[28S ribosomal RNA|28S]], [[5.8S ribosomal RNA|5.8S]], and [[18S rRNA]]s. The rRNA and RNA processing factors form large aggregates called the [[nucleolus]].<ref name="Sirri2008">{{cite journal | vauthors = Sirri V, Urcuqui-Inchima S, Roussel P, Hernandez-Verdun D | title = Nucleolus: the fascinating nuclear body | journal = Histochemistry and Cell Biology | volume = 129 | issue = 1 | pages = 13–31 | date = January 2008 | pmid = 18046571 | pmc = 2137947 | doi = 10.1007/s00418-007-0359-6 }}</ref>

In the case of transfer RNA (tRNA), for example, the 5′ sequence is removed by [[RNase P]],<ref name="pmid9759486">{{cite journal | vauthors = Frank DN, Pace NR | title = Ribonuclease P: unity and diversity in a tRNA processing ribozyme | journal = Annual Review of Biochemistry | volume = 67 | pages = 153–180 | year = 1998 | pmid = 9759486 | doi = 10.1146/annurev.biochem.67.1.153 | doi-access = free }}</ref> whereas the 3′ end is removed by the [[Ribonuclease Z|tRNase Z]] enzyme<ref name="pmid17305600">{{cite journal | vauthors = Ceballos M, Vioque A | title = tRNase Z | journal = Protein and Peptide Letters | volume = 14 | issue = 2 | pages = 137–145 | year = 2007 | pmid = 17305600 | doi = 10.2174/092986607779816050 }}</ref> and the non-templated 3′ CCA tail is added by a [[nucleotidyl transferase]].<ref name="pmid15498478">{{cite journal | vauthors = Weiner AM | title = tRNA maturation: RNA polymerization without a nucleic acid template | journal = Current Biology | volume = 14 | issue = 20 | pages = R883–R885 | date = October 2004 | pmid = 15498478 | doi = 10.1016/j.cub.2004.09.069 | doi-access = free | bibcode = 2004CBio...14.R883W }}</ref> In the case of [[miRNA|micro RNA (miRNA)]], miRNAs are first transcribed as primary transcripts or pri-miRNA with a cap and poly-A tail and processed to short, 70-nucleotide stem-loop structures known as pre-miRNA in the cell nucleus by the enzymes [[Drosha]] and [[Pasha (protein)|Pasha]]. After being exported, it is then processed to mature miRNAs in the cytoplasm by interaction with the endonuclease [[Dicer]], which also initiates the formation of the [[RNA-induced silencing complex|RNA-induced silencing complex (RISC)]], composed of the [[Argonaute]] protein.

Even snRNAs and snoRNAs themselves undergo series of modification before they become part of functional RNP complex.<ref>{{cite journal | vauthors = Bratkovič T, Božič J, Rogelj B | title = Functional diversity of small nucleolar RNAs | journal = Nucleic Acids Research | volume = 48 | issue = 4 | pages = 1627–1651 | date = February 2020 | pmid = 31828325 | pmc = 7038934 | doi = 10.1093/nar/gkz1140 }}</ref> This is done either in the nucleoplasm or in the specialized compartments called [[cajal body|Cajal bodies]].<ref>{{cite journal | vauthors = Nizami Z, Deryusheva S, Gall JG | title = The Cajal body and histone locus body | journal = Cold Spring Harbor Perspectives in Biology | volume = 2 | issue = 7 | pages = a000653 | date = July 2010 | pmid = 20504965 | pmc = 2890199 | doi = 10.1101/cshperspect.a000653 }}</ref> Their bases are methylated or pseudouridinilated by a group of [[Small Cajal body-specific RNA|small Cajal body-specific RNAs (scaRNAs)]], which are structurally similar to snoRNAs.<ref>{{cite journal | vauthors = Darzacq X, Jády BE, Verheggen C, Kiss AM, Bertrand E, Kiss T | title = Cajal body-specific small nuclear RNAs: a novel class of 2'-O-methylation and pseudouridylation guide RNAs | journal = The EMBO Journal | volume = 21 | issue = 11 | pages = 2746–2756 | date = June 2002 | pmid = 12032087 | pmc = 126017 | doi = 10.1093/emboj/21.11.2746 }}</ref>