SnRNP
From Wikipedia, the free encyclopedia
- The correct title of this article is snRNP. The initial letter is shown capitalized due to technical restrictions.
snRNPs (pronounced "snurps"), or small nuclear ribonucleoproteins, are particles that combine with pre-mRNA and various proteins to form spliceosomes (a type of large molecular complex). SnRNPs "recognize" the places along a strand of pre-mRNA and are essential in the removal of introns. These molecules are found within the cell's nucleus.
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. These molecules are usually about 150 nucleotides long. The snRNA is bound by a Ribonuclear protein (RNP) to activate its enzymatic activity.
The precise beginnings and ends of introns on the primary transcripts are marked by signals so that they can be recognized and removed. The intron-boundary signals are recognized by a short bit of RNA found in curious RNA-protein complexes known as the small nuclear ribonucleoprotein particles - snRNPs, for short. At least four different kinds of snRNPs cooperate in most splicing. The RNA in these particles is like ribosomal RNA in that it is used directly, and has both an enzymatic and a structural role.
SnRNPs were discovered by Joan A. Steitz.[1]
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[edit] Biogenesis
The RNA polymerase II transcripts U1, U2, U4 and U5 (snRNA's) acquire a m7G-cap which serves as export signal. After CRM1-mediated nuclear export, SM proteins bind to snRNA and the cap is tri-methylated. Nuclear import of these complexes is mediated by importin-beta. In the nucleus snRNPs maturate.
[edit] Notes
- ^ Lerner MR, Boyle JA, Mount SM, Wolin SL, Steitz JA, "Are snRNPs involved in splicing?", Nature Jan. 10, 1980, v. 283, no. 5743, pp. 220-224.
[edit] References
- Campbell, Neil; Reece, Jane (2002). "Chapter 17: From Gene to Protein", Biology, 6th edition, Benjamin Cummings, pg. 312.
- Joan Steitz, April 4, 2006, HHMI Review of SnRNPs, at http://www.hhmi.org/research/investigators/steitzja.html
[edit] External links
Transcription - RNA splicing (Precursor mRNA, Intron/Exon, snRNP, Spliceosome, Alternative splicing) - Polyadenylation - 5' cap
