The Formation of a Tri Snrnp Complex Containing U4 and U6 (or U4atac and U6atac) Snrnas and U5 Snrnas and Associated Proteins. This Includes Reannealing of U4 and U6 (or U4atac and U6atac) Snrnas Released From Previous Rounds of Splicing to Reform the U4/u6 Snrnp (or U4atac/u6atac Snrnp) As Well As the Subsequent Association of the U5 Snrnp with the U4/u6 Snrnp (or U4atac/u6atac Snrnp) to Form a Tri Snrnp That Is Ready to Reassemble Into Another Spliceosome Complex.
A Membrane Bounded Organelle of Eukaryotic Cells in Which Chromosomes Are Housed and Replicated. in Most Cells the Nucleus Contains All of the Cell's Chromosomes Except the Organellar Chromosomes and Is the Site of RNA Synthesis and Processing. in Some Species or in Specialized Cell Types RNA Metabolism or DNA Replication May Be Absent.
The Joining Together of Exons From One or More Primary Transcripts of Messenger RNA (mrna) and the Excision of Intron Sequences Via a Spliceosomal Mechanism So That MRNA Consisting Only of the Joined Exons Is Produced.
Any of a Series of Ribonucleoprotein Complexes That Contain Snrna(s) and Small Nuclear Ribonucleoproteins (snrnps) and Are Formed Sequentially During the Spliceosomal Splicing of One or More Substrate Rnas and Which Also Contain the RNA Substrate(s) From the Initial Target Rnas of Splicing the Splicing Intermediate Rna(s) to the Final RNA Products. During Cis Splicing the Initial Target RNA Is a Single Contiguous RNA Transcript Whether MRNA Snorna Etc. and the Released Products Are a Spliced RNA and an Excised Intron Generally As a Lariat Structure. During Trans Splicing There Are Two Initial Substrate Rnas the Spliced Leader RNA and a Pre Mrna.