Nuclear snRNA and nuclear function (discovery of 5' cap structures in RNA)

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).