Snurportin1, an m3G-cap-specific nuclear import receptor with a novel domain structure

Huber, J.; Cronshagen, Udo; Kadokura, Michinori; Marshallsay, Christopher; Wada, Takehiko; Sekine, Mitsuo; Lührmann, Reinhard

doi:10.1093/emboj/17.14.4114

Cited by 258 publications

(287 citation statements)

References 73 publications

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“…35. Alexa 488-or Cy5-labeled U1 snRNPs were prepared as described (10). Purity, functionality, and integrity of labeled U1 snRNPs were confirmed as described (36).…”

Section: Methodsmentioning

confidence: 99%

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High intranuclear mobility and dynamic clustering of the splicing factor U1 snRNP observed by single particle tracking

Kues

Dickmanns

Lührmann

et al. 2001

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

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Uridine-rich small nuclear ribonucleoproteins (U snRNPs) are components of the splicing machinery that removes introns from precursor mRNA. Like other splicing factors, U snRNPs are diffusely distributed throughout the nucleus and, in addition, are concentrated in distinct nuclear substructures referred to as speckles. We have examined the intranuclear distribution and mobility of the splicing factor U1 snRNP on a single-molecule level. Isolated U1 snRNPs were fluorescently labeled and incubated with digitoninpermeabilized 3T3 cells in the presence of Xenopus egg extract. By confocal microscopy, U1 snRNPs were found to be imported into nuclei, yielding a speckled intranuclear distribution. Employing a laser video-microscope optimized for high sensitivity and high speed, single U1 snRNPs were visualized and tracked at a spatial precision of 35 nm and a time resolution of 30 ms. The singleparticle data revealed that U1 snRNPs occurred in small clusters that colocalized with speckles. In the clusters, U1 snRNPs resided for a mean decay time of 84 ms before leaving the optical slice in the direction of the optical axis, which corresponded to a mean effective diffusion coefficient of 1 m 2 ͞s. An analysis of the trajectories of single U1 snRNPs revealed that at least three kinetic classes of low, medium, and high mobility were present. Moreover, the mean square displacements of these fractions were virtually independent of time, suggesting arrays of binding sites. The results substantiate the view that nuclear speckles are not rigid structures but highly dynamic domains characterized by a rapid turnover of U1 snRNPs and other splicing factors.T he splicing of precursor mRNA in the nucleus is catalyzed by supramolecular assemblies designated as spliceosomes, which comprise more than 70 different proteins and five uridinerich small nuclear RNAs (snRNA; ref. 1). Most of these proteins and the snRNAs are organized in the Uridine-rich small nuclear ribonucleoproteins (U snRNPs), which are classified as U1, U2, U5, and U4͞U6, according to the snRNAs they contain. The snRNAs U1, U2, U4, and U5 are synthesized in the nucleus with a 5Ј-terminal monomethyl-guanosine (m 7 G)-cap structure, transiently exported into the cytoplasm, where a common set of seven core proteins (Sm proteins) bind to the snRNAs Sm site and form a ribonucleoprotein complex called ''Sm core'' (2). Stable association of all Sm proteins is necessary for hypermethylation of the m 7 G cap to the 2,2,7-trimethyl-guanosine (m 3 G)-cap structure (3, 4). Also, several proteins associate specifically with the individual U snRNPs; in the case of U1, those proteins are 70K, U1-A, and U1-C (5). After cap modification and 3Јend processing of the snRNAs (6), the mature snRNP particles are reimported into the nucleus by import receptors. The nuclear localization signal of U1 snRNPs is complex, with the m 3 G-cap structure representing one important signaling component (7,8). A second component is located at the Sm core but has not been defined precisely yet (9). Recent...

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“…35. Alexa 488-or Cy5-labeled U1 snRNPs were prepared as described (10). Purity, functionality, and integrity of labeled U1 snRNPs were confirmed as described (36).…”

Section: Methodsmentioning

confidence: 99%

“…A second component is located at the Sm core but has not been defined precisely yet (9). Recently, an adaptor called Snurportin-1, which interacts specifically with the m 3 G cap of U snRNPs and the receptor karyopherin ␤, has been identified (10).…”

mentioning

confidence: 99%

High intranuclear mobility and dynamic clustering of the splicing factor U1 snRNP observed by single particle tracking

Kues

Dickmanns

Lührmann

et al. 2001

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

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“…In any event, the adaptor for the TMG cap is called snurportin1 (SPN1); this protein binds directly to the TMG cap and significantly improves the kinetics of snRNP import. 61,64,65 At the time, relatively little was known about the factor that mediates the interaction between the Sm core and importin b. Previous studies had indicated that the Sm core adaptor is a cytosolic factor that binds to Sm proteins and importin b.…”

Section: Smn and Cytoplasmic Snrnp Assemblymentioning

confidence: 99%

SMN - A chaperone for nuclear RNP social occasions?

2016

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Survival Motor Neuron (SMN) protein localizes to both the nucleus and the cytoplasm. Cytoplasmic SMN is diffusely localized in large oligomeric complexes with core member proteins, called Gemins. Biochemical and cell biological studies have demonstrated that the SMN complex is required for the cytoplasmic assembly and nuclear transport of Sm-class ribonucleoproteins (RNPs). Nuclear SMN accumulates with spliceosomal small nuclear (sn)RNPs in Cajal bodies, sub-domains involved in multiple facets of snRNP maturation. Thus, the SMN complex forms stable associations with both nuclear and cytoplasmic snRNPs, and plays a critical role in their biogenesis. In this review, we focus on potential functions of the nuclear SMN complex, with particular emphasis on its role within the Cajal body.

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“…Nevertheless, some nuclear proteins are known to enter the nucleus by binding to importin ␣ or ␤ via an atypical non-basic sequence (33,34). Alternatively, binding to another nuclear protein may target a protein to the nucleus (35). It is possible that AZ1 enters the nucleus via one of these mechanisms.…”

Section: Fig 7 Mutational Analysis Of Nes2mentioning

confidence: 99%

Identification of Nuclear Export Signals in Antizyme-1

Murai

Murakami

Matsufuji

2003

Journal of Biological Chemistry

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Antizyme-1 (AZ1) is a protein that negatively regulates polyamine synthesis by inhibiting the key synthetic enzyme ornithine decarboxylase and targeting it for degradation by the 26 S proteasome. Recent work shows that antizyme protein translocates to the nucleus during mouse development (Gritli-Linde, A., Nilssom, J., Bohlooly, Y. M., Heby, O., and Linde, A. (2001) Dev. Dyn. 220, 259 -275). However, the significance and mechanism of this phenomenon remain unclear. In this study, we expressed AZ1 fused with enhanced green fluorescent protein (EGFP) to study its localization in a living cell. We found that EGFP-AZ1 was predominantly localized in the cytoplasm and that treatment with leptomycin B, a specific inhibitor of chromosomal region maintenance 1 (CRM1) induced nuclear accumulation of EGFP-AZ1 in Chinese hamster ovary and NIH3T3 cells. Two independent nuclear export signal (NES) sequences, each containing essential hydrophobic residues, were identified in the 50 N-terminal amino acid residues and in the central part of AZ1. The activity of the second NES was inhibited by an N-terminal adjacent region and was only revealed in N-terminal truncated constructs. Both NESs were active when fused to an artificial nuclear protein SV40-NLS-EGFP-EGFP. The ability of AZ1 to shuttle between the nucleus and the cytoplasm suggests that it has a novel function in the nucleus.Polyamines are ubiquitous organic cations with tightly regulated cellular concentrations and are essential for cell growth and development (1, 2). Antizyme (AZ) 1 was first described as an inhibitor of ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis (3). When cellular polyamine levels rise, AZ is induced and then binds to the monomeric form of ODC (4, 5), which makes the enzyme a preferential substrate for proteolysis by the 26 S proteasome without ubiquitination (6). AZ also inhibits the uptake of extracellular polyamines (7,8). There are at least three independent antizyme isoforms conserved among mammals. AZ1 and AZ2 have a wide tissue distribution, whereas AZ3 is testis-specific (9, 10). Expression of AZs is induced by a unique translational frameshift mechanism (11). For AZ1, when cellular polyamine levels are low, the polypeptide corresponding to amino acid residues 1-68 is produced and translation is terminated at the following UGA codon (11). When cellular polyamine levels are high, ϩ1 frameshifting occurs after the 68th codon is decoded, resulting in the full-length antizyme protein (amino acid residues 1-227). All of the known regulatory activities of AZ1 are present in amino acid residues 69 -227 (12). A second AUG exists in AZ1 mRNA at the 34th codon, and this second AUG is also utilized as initiation codon (11, 13). The two resulting translation products have different half-lives (14). Furthermore, it has been suggested that the N-terminal region of the translation product from the first AUG contains a putative mitochondrial targeting signal and thus the distribution of AZ1 may depend on this region (15). It is curre...

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Snurportin1, an m3G-cap-specific nuclear import receptor with a novel domain structure

Cited by 258 publications

References 73 publications

High intranuclear mobility and dynamic clustering of the splicing factor U1 snRNP observed by single particle tracking

High intranuclear mobility and dynamic clustering of the splicing factor U1 snRNP observed by single particle tracking

SMN - A chaperone for nuclear RNP social occasions?

Identification of Nuclear Export Signals in Antizyme-1

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