Ro-Choi T S
Department of Pharmacology, Baylor College of Medicine, Houston, TX 77030, USA.
Crit Rev Eukaryot Gene Expr. 1999;9(2):107-58. doi: 10.1615/critreveukargeneexpr.v9.i2.20.
In view of the fact that eukaryotic gene expression starts in the nucleus, it is important to have a thorough understanding of nuclear macromolecular structure and function. Newly discovered snRNAs are eukaryotic cell specific and have unique subnuclear compartmental localizations. There are over 200 nucleolar-specific RNAs that include some abundant U3, U8, and U13 RNAs. Extranucleolar-nuclear-specific RNAs (snRNA) are 4.5S RNA I, II, III, 5S RNA III, U1, U2, U4, U5, and U6, in addition to over 500 different RNA species reported up to now. In particular, some snoRNAs and snRNAs have trimethylguanosine cap structures that are not present in bacteria. They have crucial roles in gene expression, such as transcription (U3 snoRNA), processing (U3, U8, U13, U14, U22, and 7-2/MRP), methylation (U14-16, U18, U20-21, and U24-63), pseudouridylation (E2, E3, U19, U23, and U64-72), and hnRNA splicing (U1, U2, U4, U5, and U6 snRNA).
鉴于真核基因表达始于细胞核，全面了解核大分子的结构和功能非常重要。新发现的小核仁RNA（snRNA）具有真核细胞特异性，且在亚核区室中有独特的定位。有超过200种核仁特异性RNA，包括一些丰富的U3、U8和U13 RNA。核仁外核特异性RNA（snRNA）有4.5S RNA I、II、III、5S RNA III、U1、U2、U4、U5和U6，此外还有迄今报道的500多种不同的RNA种类。特别地，一些小核仁RNA和小核RNA具有细菌中不存在的三甲基鸟苷帽结构。它们在基因表达中发挥关键作用，如转录（U3小核仁RNA）、加工（U3、U8、U13、U14、U22和7-2/MRP）、甲基化（U14-16、U18、U20-21和U24-63）、假尿苷化（E2、E3、U19、U23和U64-72）以及核不均一RNA剪接（U1、U2、U4、U5和U6小核RNA）。
