snRNPs (pronounced "snurps"), or mall uclear iboucleoroteins, are RNA-protein complexes that combine with unmodified pre-mRNA and various other proteins to form a spliceosome, a large RNA-protein molecular complex upon which splicing of pre-mRNA occurs. The action of snRNPs is essential to the removal of introns from pre-mRNA, a critical aspect of post-transcriptional modification of RNA, occurring only in the nucleus of eukaryotic cells.
Additionally, U7 snRNP is not involved in splicing at all, as U7 snRNP is responsible for processing the 3′ stem-loop of histone pre-mRNA.
The two essential components of snRNPs are protein molecules and RNA. The RNA found within each snRNP particle is known as small nuclear RNA, or snRNA, and is usually about 150 nucleotides in length. The snRNA component of the snRNP gives specificity to individual introns by "recognizing" the sequences of critical splicing signals at the 5 and 3 ends and branch site of introns. The snRNA in snRNPs is similar to ribosomal RNA in that it directly incorporates both an enzymatic and a structural role.
SnRNPs were discovered by Michael R. Lerner and Joan A. Steitz.
Thomas R. Cech and Sidney Altman also played a role in the discovery, winning the Nobel Prize for Chemistry in 1989 for their independent discoveries that RNA can act as a catalyst in cell development.