PRP4 (RNA4) from Saccharomyces cerevisiae: its gene product is associated with the U4/U6 small nuclear ribonucleoprotein particle

Electron microscopy of small nuclear ribonucleoprotein (snRNP) particles U2 and U5: evidence for a common structure-determining principle in the major U snRNP family

We have studied by electron microscopy the structures of native small nuclear ribonucleoprotein (snRNP) particles U2 and U5 from HeLa cells. The structure of native U2 snRNP is characterized by a main body 8 nm in diameter with one additional domain about 4 nm long and 6 nm wide. Electron micrographs show that the 20S U5 snRNP, which contains at least seven U5-specific proteins in addition to the common proteins, has an elongated structure measuring 20-23 nm in length and 11-14 nm in width. Two main structural domains can be distinguished: a small head and a large elongated body about twice the size of the head. In addition to the head, the body of the 20S U5 snRNP possesses three short protuberances. The U2 and U5 core RNP particles--that is, of the snRNPs U2 and U5 without the snRNP-specific proteins, look much simpler and smaller under the electron microscope. They both are round in shape with a diameter of approximately 8 nm. With respect to their size, appearance, and fine structure, the U2 and U5 snRNP cores not only closely resemble each other but also share these properties with the core domain of U1 snRNP. We propose that the characteristic shape of each of the major snRNP species U1, U2, U4/U6, and U5 is determined by (i) a core domain containing the proteins that are common to all members of this family, which has the same shape for each member, and (ii) peripheral structures, which for snRNPs U1, U2, and U5 arise from the specific proteins, that give each of these snRNP species its characteristic shape.

The PRP4 (RNA4) protein of Saccharomyces cerevisiae is associated with the 5' portion of the U4 small nuclear RNA

We have combined oligonucleotide-directed RNase H degradation and immunoprecipitation in a study of the association of the Saccharomyces cerevisiae PRP4 protein with the U4-U6 complex. We have found that three oligonucleotides were able to direct nearly to completion the RNase H-specific cleavage of the target RNA molecules as they exist in splicing extracts. Immunoprecipitation of the degradation products with PRP4 antibody showed that the 5' portion of U4 small nuclear RNA (snRNA) and the 3' portion of U6 snRNA coimmunoprecipitated with the PRP4 protein. Micrococcal nuclease protection experiments confirmed further that the 5' portion and 3' end of U4 snRNA were very resistant to nuclease digestion, whereas the 3' portion of U6 snRNA was protected to only a very small extent. We conclude that the PRP4 protein of S. cerevisiae is associated primarily with the 5' portion of U4 snRNA in the U4-U6 small nuclear ribonucleoprotein (snRNP).

The mammalian analogue of the yeast PRP8 splicing protein is present in the U4/5/6 small nuclear ribonucleoprotein particle and the spliceosome

HeLa cell nuclear extracts contain a protein reactive with antibodies against PRP8, a polypeptide essential for pre-mRNA splicing in yeast and a specific component of the yeast U5 small nuclear ribonucleoprotein (snRNP) [Lossky, M., Anderson, G. J., Jackson, S. P. & Beggs, J. (1987) Cell 51, 1019-1026]. The mammalian protein appears as a doublet at approximately 200 kDa, smaller than the 260-kDa yeast protein, and possesses an Sm epitope as determined by immunoblotting. Its association with a snRNP of the Sm class other than U1 or U2 is indicated by its immunoprecipitation by anti-Sm and anti-trimethylguanosine antibodies but not by anti-(U1) or anti-(U2) RNP sera. Gradient fractionation of splicing extracts demonstrates that the 200-kDa protein is a component of the U4/5/6 snRNP complex and of U5 snRNPs. It is also present in affinity-purified spliceosomes.