SnRNP

Stevens SW et al Composition and functional characterization of the yeast spliceosomal penta-snRNP. Mol Cell 2002 9 31-Tucker M, Parker R Mechanisms and control of mRNA decapping in Saccharomyces cerevisiae. Ann Rev Biochem 2000 69 571. 

Benzophenone-4-iodoacetamide has been used to study the 100-KDa U5 snRNP protein (hPrp28p) and its interactions (Ismaili et al., 2001). 

U snRNPs) Sm proteins and trimethylguanosine Gap structure of RNA Importin /3/Snurportin... 

Introns are removed from hnRNA by splicing, accomplished by spliceosomes (also known as an snRNP, or snurp), which are complexes of snRNA and protein. The hnRNA molecule is cut at splice sites at the 5 (donor) and 3 (acceptor) ends of the intron. The intron is excised in the form of a lariat structuie and degraded. Neighboring exons are joined together to assemble the coding region of the mature mRNA. 

Splicing occurs in a large protein-nucleic acid complex, termed the spUceosome. Components of the spliceosome are, apart from the pre-mRNA, a number of proteins and small RNAs, termed the Ul, U2, U4, U5 and U6. The RNAs found in the spUceo-some are bound to specific proteins. The complexes are termed snRNPs (small nuclear ribonucleoprotein). Depending upon the type of RNA bound, there are Ul, U2, U5 and U4/U6 snRNPs. 

Spliceosomal introns generally have the dinucleotide sequence GU and AG at the 5 and 3 ends, respectively, and these sequences mark the sites where splicing occurs. The Ul snRNA contains a sequence complementary to sequences near the 5 splice site of nuclear mRNA introns (Fig. 26-16a), and the Ul snRNP... 

Removal of introns. snRNP = small nuclear ribonucleoprotein particle. 

Patients with the autoimmune disease systemic lupus erythematosus make autoantibodies directed against the Sm proteins of snRNP particles.552,553 Antibodies from different patients vary in tiieir specificities, making these antibodies a useful tool in the isolation and study of snRNAs and their protein complexes.552,554... 

Figure 28-22 Assembly and action of the spliceosomal complex. Four special sequence elements control the process the 5 and 3 splice sites, the branch point (adenosine A), and a polypyrimidine tract. The snRNP particle U1 locates the 5 splice site and U2 the branch point. The tri-snRNP U4 U6 U5 then binds, U6 recognizing the 5 splice site, and U1 and U4 are released. The 2 -OH of the branch point adenosine attacks the phos-phodiester linkage to form a lariet intermediate, which releases the intron in a lariet form in the final step. After Valcarcel and Green.612...

The spliceosome. The hnRNA of nuclei, which includes all of the pre-mRNA, is associated with proteins, which sometimes form very large 200S particles.604 After limited cleavage with nucleases they tend to sediment in the 30S-40S range and to contain a variety of proteins.605 606 Some of the proteins may have been involved in control of transcription.606 Others participate in splicing. The smaller snRNP particles then appear to come into the nucleus and displace much, but not all, of the protein present in the pre-mRNA ribonucleoprotein particles.605... 

After the U1 snRNP binds to the pre-mRNA (step a, Fig. 28-22)614 the U2 snRNP binds to another almost invariant sequence CURACU found 20 to 55 nucleotides upstream of the 3 junction.608,615-617 The A in this sequence becomes a branch point. It is brought close to the 5 splice site with the aid of a preassembled complex of snRNPs U4, U6, and U5. In this complex U4 and U6 are tightly paired, additional proteins are also present,618 21 and enhancers may be located in adjacent exons.617 Upon binding of U6 to the 5 splice site, the U1 and U4 snRNPs are released (step b, Fig. 28-22) and the 2 -OH of the branch point adenosine attacks the backbone phosphorus atom (step c) at the 5 splice junction forming a lariat intermediate. The 3 end created at the 5 junction must now be held and brought close to the 3 splice junction, which is located with the aid of U5 snRNP.622 The 3 splice junction, utilized in the second splicing step (step d, Fig. 28-22) has the consensus sequence (T/C)N(C/T)AG G. 

A small fraction of eukaryotic mRNA introns are characterized by AU and AC (rather than GU and AG) ends. The spliceosomes that act on these introns contain modified snRNAs U4 and U6, which are designated U4 ., and U6.,f.,.. They also require Ull and U12 snRNPs.534 625 626... 

To assist in the modification and processing of mRNAs, eukaryotic cells contain in their nuclei small nuclear RNAs (snRNAs), which are complexed with specific proteins to form small nuclear ribonucleoprotein particles (snRNPs). These RNAs have been named U1, U2, U3,.. . , U13 and range in size from 100 to 220 bases. One, U3, is... 

Tsai, D.E., Harper, D.S. and Keene, J.D. (1991) Ul-snRNP-A protein selects a ten nucleotide consensus sequence from a degenerate RNA pool presented in various structural... 

The most recent of these is the four-way helical RNA junction found in the U1 snRNP Nagai and coworkers (Pomeranz-Krummel el al.,... 

K9. Koren, E., Koscec, M., Wolfson-Reichlin, M., Ebling, F. M., Tsao, B., etal., Murine and human antibodies to native DNA that cross-react with the A and D SnRNP polypeptides cause direct injury of cultured kidney cells. J. Immunol. 154, 4857-4864 (1995). 

U2. Utz, R J., Hottelet, M., van Venrooij, W. J., and Anderson, P., Association of phosphorylated serine/arginine (SR) splicing factors with the U1-small ribonucleoprotein (snRNP) autoantigen complex accompanies apoptotic cell death. J. Exp. Med. 187, 547—560 (1998). 

NADH nicotinamide adenine dinucleotide snRNP small nuclear ribonucleoprotein... 

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