Editing MicroRNA (section)

===Transcription===
miRNA genes are usually transcribed by [[RNA polymerase II]] (Pol II).<ref name="LeeEMBO">{{cite journal | vauthors = Lee Y, Kim M, Han J, Yeom KH, Lee S, Baek SH, Kim VN | title = MicroRNA genes are transcribed by RNA polymerase II | journal = The EMBO Journal | volume = 23 | issue = 20 | pages = 4051–60 | date = October 2004 | pmid = 15372072 | pmc = 524334 | doi = 10.1038/sj.emboj.7600385 }}</ref><ref name="Zhou_2007">{{cite journal | vauthors = Zhou X, Ruan J, Wang G, Zhang W | title = Characterization and identification of microRNA core promoters in four model species | journal = PLOS Computational Biology | volume = 3 | issue = 3 | pages = e37 | date = March 2007 | pmid = 17352530 | pmc = 1817659 | doi = 10.1371/journal.pcbi.0030037 | bibcode = 2007PLSCB...3...37Z | doi-access = free }}</ref> The polymerase often binds to a promoter found near the DNA sequence, encoding what will become the hairpin loop of the pre-miRNA. The resulting transcript is [[5' cap|capped]] with a specially modified nucleotide at the 5' end, [[Polyadenylation|polyadenylated]] with multiple [[Adenosine monophosphate|adenosines]] (a poly(A) tail),<ref name=LeeEMBO/><ref name="Cai_2004">{{cite journal | vauthors = Cai X, Hagedorn CH, Cullen BR | title = Human microRNAs are processed from capped, polyadenylated transcripts that can also function as mRNAs | journal = RNA | volume = 10 | issue = 12 | pages = 1957–66 | date = December 2004 | pmid = 15525708 | pmc = 1370684 | doi = 10.1261/rna.7135204 }}</ref> and [[RNA splicing|spliced]]. Animal miRNAs are initially transcribed as part of one arm of an ~80 nucleotide RNA [[stem-loop|hairpin]] that in turn forms part of a several hundred nucleotide-long miRNA precursor termed a pri-miRNA.<ref name=LeeEMBO/><ref name="Cai_2004"/> When a hairpin precursor is found in the 3' UTR, a transcript may serve as a pri-miRNA and a mRNA.<ref name="Cai_2004"/> [[RNA polymerase III]] (Pol III) transcribes some miRNAs, especially those with upstream [[Alu sequence]]s, [[transfer RNA]]s (tRNAs), and [[mammalian wide interspersed repeat]] (MWIR) promoter units.<ref name="pmid18778799">{{cite journal | vauthors = Faller M, Guo F | title = MicroRNA biogenesis: there's more than one way to skin a cat | journal = Biochimica et Biophysica Acta (BBA) - Gene Regulatory Mechanisms | volume = 1779 | issue = 11 | pages = 663–67 | date = November 2008 | pmid = 18778799 | pmc = 2633599 | doi = 10.1016/j.bbagrm.2008.08.005 }}</ref>