The Cytoplasmic Sites of the snRNP Protein Complexes Are Punctate Structures That Are Responsive to Changes in Metabolism and Intracellular Architecture

Zieve, Gary W.

doi:10.1006/excr.1998.4354

Cited by 6 publications

(9 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…6B). It is interesting to compare such yeast sites of staining with the described discrete punctuate sites observed recently in mammalian fibroblasts in immunofluorescence microscopic studies using five anti-Sm monoclonal antibodies (72). In these studies, dots, distributed extensively and evenly in the cytoplasm, are visible in addition to the expected intense nuclear staining representing the speckled distribution of snRNP proteins in the nucleus.…”

Section: Discussionmentioning

confidence: 72%

“…In these studies, dots, distributed extensively and evenly in the cytoplasm, are visible in addition to the expected intense nuclear staining representing the speckled distribution of snRNP proteins in the nucleus. These cytoplasmic punctuated sites may reflect the cytoplasmic pools of snRNP core proteins and represent storage particles of the snRNP core protein complexes or staging centers for snRNP core particle assembly (72). It is tempting to suggest that the fluorescent sites observed for the yeast GFP-SmB alleles mutated in the NLS-like motif may also represent storage and/or assembly structures for yeast Sm core particles.…”

Section: Discussionmentioning

confidence: 99%

“…In the nucleus, in addition to a diffuse nucleoplasmic snRNP staining, the snRNP particles are localized in speckles, coiled bodies, and nucleoli (6,30,65,66). The snRNP protein complexes are also localized into the cytoplasmic compartment as discrete punctuate structures which are uniformly distributed and which may represent storage particles of the snRNP core protein complexes or staging centers for snRNP core particle assembly (72).…”

mentioning

confidence: 99%

See 2 more Smart Citations

Functional Characterization of Nuclear Localization Signals in Yeast Sm Proteins

Bordonne

2000

Molecular and Cellular Biology

View full text Add to dashboard Cite

In mammals, nuclear localization of U-snRNP particles requires the snRNA hypermethylated cap structure and the Sm core complex. The nature of the signal located within the Sm core proteins is still unknown, both in humans and yeast. Close examination of the sequences of the yeast SmB, SmD1, and SmD3 carboxylterminal domains reveals the presence of basic regions that are reminiscent of nuclear localization signals (NLSs). Fluorescence microscopy studies using green fluorescent protein (GFP)-fusion proteins indicate that both yeast SmB and SmD1 basic amino acid stretches exhibit nuclear localization properties. Accordingly, deletions or mutations in the NLS-like motifs of SmB and SmD1 dramatically reduce nuclear fluorescence of the GFP-Sm mutant fusion alleles. Phenotypic analyses indicate that the NLS-like motifs of SmB and SmD1 are functionally redundant: each NLS-like motif can be deleted without affecting yeast viability whereas a simultaneous deletion of both NLS-like motifs is lethal. Taken together, these findings suggest that, in the doughnut-like structure formed by the Sm core complex, the carboxyl-terminal extensions of Sm proteins may form an evolutionarily conserved basic amino acid-rich protuberance that functions as a nuclear localization determinant.Splicing of nuclear pre-mRNAs in yeast and mammals occurs in the multicomponent complex called the spliceosome whose formation involves the ordered assembly of the U1, U2, and U4/U6.U5 snRNPs, together with a multitude of nonsnRNP-associated protein factors on the pre-mRNA substrate (27, 67). In both systems, except for the U6 snRNP, each particle is composed of a U snRNA, a set of specific proteins associated with one particular snRNP, and a set of common (or core) proteins shared by all snRNPs. This last group is composed of the Sm proteins B, BЈ (in mammals), D1, D2, D3, E, F, and G, which assemble around the Sm site of the snRNA (34). In addition to the common Sm core proteins, the yeast and metazoan U6, U4/U6, and U4/U6.U5 snRNPs also contain seven distinct proteins called Lsm (like Sm) exhibiting clear homology to the Sm proteins (1,7,19,21,39,55,62,68).The Sm and Lsm proteins are highly conserved in all eukaryotic organisms. They contain the Sm domain, which consists of two conserved regions separated by a linker of variable length. Seven residues are highly conserved, and at many positions, the physicochemical property of the amino acid is maintained (7,21,62). The Sm motif is important for Sm protein function. Indeed, mutations at various positions in this motif, and mostly the hydrophobic conserved residues, abolish protein-protein interactions between Sm partners and hinder Sm core RNP complex formation (5, 21). Based on the crystal structures of two human Sm protein complexes (SmB/SmD3 and SmD1/SmD2), a model in which the seven Sm proteins form a doughnut-like structure has been proposed (26).Assembly of the eukaryotic U snRNPs is a multistep process following an ordered pathway (36, 47). After transcription by RNA polymerase II, the snRNAs ...

show abstract

Section: Discussionmentioning

confidence: 72%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Functional Characterization of Nuclear Localization Signals in Yeast Sm Proteins

Bordonne

2000

Molecular and Cellular Biology

View full text Add to dashboard Cite

show abstract

“…We are aware of only one earlier study in which U bodies may have been observed. Zieve (22) showed that snRNP proteins are localized in punctate structures in the cytoplasm of cultured hamster fibroblasts, especially after hypertonic treatment. His study did not include an examination of snRNAs or other proteins involved in snRNP assembly.…”

Section: Resultsmentioning

confidence: 99%

U bodies are cytoplasmic structures that contain uridine-rich small nuclear ribonucleoproteins and associate with P bodies

Liu

Gall

2007

Proc. Natl. Acad. Sci. U.S.A.

119

110

View full text Add to dashboard Cite

Uridine-rich small nuclear ribonucleoproteins (U snRNPs) are involved in key steps of pre-mRNA processing in the nucleus of eukaryotic cells. U snRNPs are enriched in the nucleus in discrete organelles that include speckles, Cajal bodies, and histone locus bodies. However, most U snRNPs are assembled in the cytoplasm, not in the nucleus. Despite extensive biochemical information, little is known about the spatial organization of U snRNPs in the cytoplasm. Here we show that U snRNPs in Drosophila are concentrated in discrete cytoplasmic structures, which we call U bodies, because they contain the major U snRNPs. In addition to snRNPs, U bodies contain essential snRNP assembly factors, suggesting that U bodies are sites for assembly or storage of snRNPs before their import into the nucleus. U bodies invariably associate with P bodies, which are involved in RNA surveillance and decay. Genetic disruption of P body components affects the organization of U bodies, suggesting that the two cytoplasmic bodies may cooperate in regulating aspects of snRNP metabolism. The identification of U bodies provides an opportunity to correlate specific biochemical steps of snRNP biogenesis with structural features of the cytoplasm.Cajal body ͉ histone locus body ͉ Drosophila ͉ SMN ͉ snRNP R NAs synthesized in the nucleus of eukaryotic cells almost invariably undergo processing before they are sent to their final destination. Processing can involve cleavage of a precursor molecule, removal of parts of the precursor, or modification of specific bases or sugars. The processing machinery consists of small RNAs (usually Ͻ300 nucleotides) associated with specific proteins. The U1, U2, U4/U6, and U5 small nuclear ribonucleoproteins (snRNPs) are major components of the spliceosome, the complex that removes introns from the majority of premRNAs (1-3). The U7 snRNP specifically carries out 3Ј cleavage of intronless histone pre-mRNAs (4, 5). Each snRNP contains a small RNA associated with a ring of seven Sm/Lsm proteins and one or more snRNP-specific proteins (4, 6, 7). As their name implies, snRNPs function in the nucleus, where they are enriched in discrete nuclear organelles that include speckles (8, 9), Cajal bodies (10, 11), and histone locus bodies (12). However, it has been known for a long time that most snRNPs are assembled in the cytoplasm (13), and properly assembled Sm cores are required for snRNP import into the nucleus (14). Nevertheless, little is known about the spatial organization of snRNPs in the cytoplasm.We used the Drosophila ovary as a model system to investigate the organization of cellular snRNPs. The Drosophila ovary contains egg chambers in various stages of development, from the beginning of meiosis to the fully formed oocyte ready for fertilization and egg laying. Each egg chamber contains a developing oocyte and 15 associated nurse cells. For our purposes, the large size of the nurse cells and their polyploid nuclei facilitates study of the snRNPs by immunofluorescent staining and in situ hybridization. Ovarian de...

show abstract

“…The major snRNP particles contain at least 50 'core' or RNA-specific proteins [30]. There are four major snRNP particles (U1, U2, U4 and U5/U6) and a large body of other less abundant particles in the nucleoplasm [31]. Consequently, co-localization of spartin with α-Sm may indicate its association with this complex and a functional role in the nucleus.…”

Section: Spartin Co-localizes With Snrnp In the Nucleus In Human And mentioning

confidence: 98%

Endogenous spartin, mutated in hereditary spastic paraplegia, has a complex subcellular localization suggesting diverse roles in neurons

Robay

Patel

Simpson

et al. 2006

Experimental Cell Research

View full text Add to dashboard Cite

The Cytoplasmic Sites of the snRNP Protein Complexes Are Punctate Structures That Are Responsive to Changes in Metabolism and Intracellular Architecture

Cited by 6 publications

References 27 publications

Functional Characterization of Nuclear Localization Signals in Yeast Sm Proteins

Functional Characterization of Nuclear Localization Signals in Yeast Sm Proteins

U bodies are cytoplasmic structures that contain uridine-rich small nuclear ribonucleoproteins and associate with P bodies

Endogenous spartin, mutated in hereditary spastic paraplegia, has a complex subcellular localization suggesting diverse roles in neurons

Contact Info

Product

Resources

About