Editing Primary transcript (section)

== Research ==

5-[[Fluorouracil]] (FUra) exposure in [[methotrexate]]-resistant KB cells led to a two-fold reduction in total [[dihydrofolate reductase]] (DHFR) mRNA levels, while the level of DHFR pre-mRNA with certain introns remained unaffected. The half-life of DHFR mRNA or pre-mRNA did not change significantly, but the transition rate of DHFR RNA from the nucleus to the cytoplasm decreased, suggesting that FUra may influence mRNA processing and/or nuclear DHFR mRNA stability.<ref>{{cite journal | title = 5-Fluorouracil inhibits dihydrofolate reductase precursor mRNA processing and/or nuclear mRNA stability in methotrexate-resistant KB cells | journal = The Journal of Biological Chemistry | volume = 264 | issue = 35 | pages = 21413–21 | date = December 1989 | doi = 10.1016/S0021-9258(19)30096-1 | pmid = 2592384 | doi-access = free | vauthors = Will CL, Dolnick BJ }}</ref>

In ''[[Drosophila]]'' and ''[[Aedes]]'', hnRNA (pre-mRNA) size was larger in ''Aedes'' due to its larger genome, despite both species producing mature mRNA of similar size and sequence complexity. This indicates that hnRNA size increases with genome size.<ref>{{cite journal | title = hnRNA size and processing as related to different DNA content in two dipterans: Drosophila and Aedes | journal = Cell | volume = 5 | issue = 3 | pages = 281–90 | date = July 1975 | pmid = 807333 | doi = 10.1016/0092-8674(75)90103-8 | s2cid = 39038640 | vauthors = Lengyel J, Penman S }}</ref>

In [[HeLa cell]]s, spliceosome groups on pre-mRNA were found to form within [[nuclear speckles]], with this formation being temperature-dependent and influenced by specific RNA sequences. Pre-mRNA targeting and splicing factor loading in speckles were critical for spliceosome group formation, resulting in a speckled pattern.<ref>{{cite journal | title = Prespliceosomal assembly on microinjected precursor mRNA takes place in nuclear speckles | journal = Molecular Biology of the Cell | volume = 12 | issue = 2 | pages = 393–406 | date = February 2001 | pmid = 11179423 | doi = 10.1091/mbc.12.2.393 | citeseerx = 10.1.1.324.8865 | pmc = 30951 | vauthors = Melčák I, Melčáková Š, Kopsky V, Večeřová J, Raška I }}</ref>

Recruiting pre-mRNA to nuclear speckles significantly increased splicing efficiency and protein levels, indicating that proximity to speckles enhances splicing efficiency.<ref>{{cite journal | title = Genome organization around nuclear speckles drives mRNA splicing efficiency. | journal = Nature | volume = 629 | issue = 8014 | pages = 1165–1173 | date = May 2024 | pmid = 38720076 | pmc = 11164319 | doi = 10.1038/s41586-024-07429-6 | bibcode = 2024Natur.629.1165B | vauthors = Bhat P, Chow A, Emert B, Ettlin O, Quinodoz SA, Strehle M, Takei Y, Burr A, Goronzy IN, Chen AW, Huang W, Ferrer JL, Soehalim E, Goh S, Chari T, Sullivan DK, Blanco MR, Guttman M }}</ref>