scholarly journals Nup124p Is a Nuclear Pore Factor ofSchizosaccharomyces pombe That Is Important for Nuclear Import and Activity of Retrotransposon Tf1

1999 ◽  
Vol 19 (8) ◽  
pp. 5768-5784 ◽  
Author(s):  
David Balasundaram ◽  
Michael J. Benedik ◽  
Mary Morphew ◽  
Van-Dinh Dang ◽  
Henry L. Levin
Keyword(s):  
Nuclear Localization ◽  
Nuclear Import ◽  
Direct Interaction ◽  
Host Factors ◽  
Nuclear Pore ◽  
Cytoplasmic Localization ◽  
Hybrid Analysis ◽  
Localization Signal ◽  
Two Hybrid

ABSTRACT The long terminal repeat (LTR)-containing retrotransposon Tf1 propagates within the fission yeast Schizosaccharomyces pombe as the result of several mechanisms that are typical of both retrotransposons and retroviruses. To identify host factors that contribute to the transposition process, we mutagenized cultures ofS. pombe and screened them for strains that were unable to support Tf1 transposition. One such strain contained a mutation in a gene we named nup124. The product of this gene contains 11 FXFG repeats and is a component of the nuclear pore complex. In addition to the reduced levels of Tf1 transposition, thenup124-1 allele caused a significant reduction in the nuclear localization of Tf1 Gag. Surprisingly, the mutation innup124-1 did not cause any reduction in the growth rate, the nuclear localization of specific nuclear localization signal-containing proteins, or the cytoplasmic localization of poly(A) mRNA. A two-hybrid analysis and an in vitro precipitation assay both identified an interaction between Tf1 Gag and the N terminus of Nup124p. These results provide evidence for an unusual mechanism of nuclear import that relies on a direct interaction between a nuclear pore factor and Tf1 Gag.

Nuclear import of glycoconjugates is distinct from the classical NLS pathway

1995 ◽  
Vol 108 (4) ◽  
pp. 1325-1332 ◽  
Author(s):  
E. Duverger ◽  
C. Pellerin-Mendes ◽  
R. Mayer ◽  
A.C. Roche ◽  
M. Monsigny
Keyword(s):  
Nuclear Localization ◽  
Nuclear Import ◽  
Nuclear Localization Signal ◽  
Peptide Sequence ◽  
Nuclear Pore ◽  
Dependent Manner ◽  
Permeabilized Cells ◽  
Localization Signal ◽  
Energy Dependent ◽  
Cytosolic Factors

The nuclear import of many proteins depends on a short peptide sequence called the nuclear localization signal. However, glycosylated proteins, which lack such a nuclear localization signal, upon their injection into the cytosol by electroporation, enter the nucleus in a sugar-dependent manner. This paper brings new insights on the mechanism of this process, based on a study of neoglycoprotein nuclear uptake by digitonin-permeabilized cells. The nuclear import of neoglycoproteins is energy dependent: it does not occur when cells are maintained at 4 degrees C or when cells are ATP-depleted by treatment with apyrase. The nuclear import of neoglycoproteins occurs through the nuclear pore: it is inhibited by preincubation of cells with wheat germ agglutinin, a lectin which binds the nuclear pore glycoproteins and blocks the translocation step of nuclear localization signal bearing proteins through the nuclear pore. Furthermore, the nuclear import of neoglycoproteins does not use the pathway of nuclear localization signal bearing proteins: nuclear import of nuclear localization signal bearing proteins depends on cytosolic factors and is inhibited by treatment of cells with N-ethylmaleimide, while the nuclear import of neoglycoproteins neither requires added cytosolic factors nor is sensitive to alkylation by N-ethylmaleimide. In addition, upon incubation in the presence of a large excess of nuclear localization signal bearing protein, the nuclear import of neoglycoproteins is not inhibited.

scholarly journals Nuclear Localization Signal and Protein Context both Mediate Importin α Specificity of Nuclear Import Substrates

2006 ◽  
Vol 26 (23) ◽  
pp. 8697-8709 ◽  
Author(s):  
Beate Friedrich ◽  
Christina Quensel ◽  
Thomas Sommer ◽  
Enno Hartmann ◽  
Matthias Köhler
Keyword(s):  
Nuclear Localization ◽  
Nuclear Import ◽  
Nuclear Localization Signal ◽  
Protein Import ◽  
Binding Studies ◽  
Vitro Binding ◽  
Importin Α ◽  
Localization Signal ◽  
Experimental Approaches

ABSTRACT The “classical” nuclear protein import pathway depends on importin α and importin β. Importin α binds nuclear localization signal (NLS)-bearing proteins and functions as an adapter to access the importin β-dependent import pathway. In humans, only one importin β is known to interact with importin α, while six α importins have been described. Various experimental approaches provided evidence that several substrates are transported specifically by particular α importins. Whether the NLS is sufficient to mediate importin α specificity is unclear. To address this question, we exchanged the NLSs of two well-characterized import substrates, the seven-bladed propeller protein RCC1, preferentially transported into the nucleus by importin α3, and the less specifically imported substrate nucleoplasmin. In vitro binding studies and nuclear import assays revealed that both NLS and protein context contribute to the specificity of importin α binding and transport.

Nuclear import of protein kinase C occurs by a mechanism distinct from the mechanism used by proteins with a classical nuclear localization signal

1998 ◽  
Vol 111 (13) ◽  
pp. 1823-1830 ◽  
Author(s):  
D. Schmalz ◽  
F. Hucho ◽  
K. Buchner
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Nuclear Localization ◽  
Phorbol Ester ◽  
Nuclear Import ◽  
Nuclear Localization Signal ◽  
Nuclear Pore ◽  
Kinase C ◽  
Localization Signal ◽  
Protein Kinase C Alpha

Protein kinase C does not have any known nuclear localization signal but, nevertheless, is redistributed from the cytoplasm to the nucleus upon various stimuli. In NIH 3T3 fibroblasts stimulation with phorbol ester leads to a translocation of protein kinase C alpha to the plasma membrane and into the cell nucleus. We compared the mechanism of protein kinase C alpha's transport into the nucleus with the transport mechanism of a protein with a classical nuclear localization signal at several steps. To this end, we co-microinjected fluorescently labeled bovine serum albumin to which a nuclear localization signal peptide was coupled, together with substances interfering with conventional nuclear protein import. Thereafter, the distribution of both the nuclear localization signal-bearing reporter protein and protein kinase C alpha was analyzed in the same cells. We can show that, in contrast to the nuclear localization signal-dependent transport, the phorbol ester-induced transport of protein kinase C alpha is not affected by microinjection of antibodies against the nuclear import factor p97/importin/karyopherin beta or microinjection of non-hydrolyzable GTP-analogs. This suggests that nuclear import of protein kinase C alpha is independent of p97/importin/karyopherin beta and independent of GTP. At the nuclear pore there are differences between the mechanisms too, since nuclear transport of protein kinase C alpha cannot be inhibited by wheat germ agglutinin or an antibody against nuclear pore complex proteins. Together these findings demonstrate that the nuclear import of protein kinase C alpha occurs by a mechanism distinct from the one used by classical nuclear localization signal-bearing proteins at several stages.

scholarly journals Identification and Functional Characterization of a Novel Nuclear Localization Signal Present in the Yeast Nab2 Poly(A)+ RNA Binding Protein

1998 ◽  
Vol 18 (3) ◽  
pp. 1449-1458 ◽  
Author(s):  
Ray Truant ◽  
Robert A. Fridell ◽  
R. Edward Benson ◽  
Hal Bogerd ◽  
Bryan R. Cullen
Keyword(s):  
Nuclear Localization ◽  
Nuclear Import ◽  
Nuclear Localization Signal ◽  
Nuclear Export ◽  
Mammalian Cells ◽  
Rna Binding ◽  
Yeast Cells ◽  
Vitro Assay ◽  
Localization Signal

ABSTRACT The nuclear import of proteins bearing a basic nuclear localization signal (NLS) is dependent on karyopherin α/importin α, which acts as the NLS receptor, and karyopherin β1/importin β, which binds karyopherin α and mediates the nuclear import of the resultant ternary complex. Recently, a second nuclear import pathway that allows the rapid reentry into the nucleus of proteins that participate in the nuclear export of mature mRNAs has been identified. In mammalian cells, a single NLS specific for this alternate pathway, the M9 NLS of heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1), has been described. The M9 NLS binds a transport factor related to karyopherin β1, termed karyopherin β2 or transportin, and does not require a karyopherin α-like adapter protein. A yeast homolog of karyopherin β2, termed Kap104p, has also been described and proposed to play a role in the nuclear import of a yeast hnRNP-like protein termed Nab2p. Here, we define a Nab2p sequence that binds to Kap104p and that functions as an NLS in both human and yeast cells despite lacking any evident similarity to basic or M9 NLSs. Using an in vitro nuclear import assay, we demonstrate that Kap104p can direct the import into isolated human cell nuclei of a substrate containing a wild-type, but not a defective mutant, Nab2p NLS. In contrast, other NLSs, including the M9 NLS, could not function as substrates for Kap104p. Surprisingly, this in vitro assay also revealed that human karyopherin β1, but not the Kap104p homolog karyopherin β2, could direct the efficient nuclear import of a Nab2p NLS substrate in vitro in the absence of karyopherin α. These data therefore identify a novel NLS sequence, active in both yeast and mammalian cells, that is functionally distinct from both basic and M9 NLS sequences.

scholarly journals The cell cycle-dependent nuclear import of v-Jun is regulated by phosphorylation of a serine adjacent to the nuclear localization signal.

1995 ◽  
Vol 130 (2) ◽  
pp. 255-263 ◽  
Author(s):  
T Tagawa ◽  
T Kuroki ◽  
P K Vogt ◽  
K Chida
Keyword(s):  
Cell Cycle ◽  
Nuclear Localization ◽  
Nuclear Import ◽  
Nuclear Localization Signal ◽  
Protein Kinase Inhibitors ◽  
Nuclear Accumulation ◽  
Dependent Manner ◽  
Localization Signal ◽  
Cycle Dependent

Cell cycle-dependent phosphorylation and nuclear import of the tumorigenic transcription factor viral Jun (v-Jun) were investigated in chicken embryo fibroblasts. Nuclear accumulation of v-Jun but not of cellular Jun (c-Jun) is cell cycle dependent, decreasing in G1 and increasing in G2. The cell cycle-dependent regulation of v-Jun was mapped to a single serine residue at position 248 (Ser248), adjacent to the nuclear localization signal (NLS). Ser248 of v-Jun represents an amino acid substitution, replacing cysteine of c-Jun. It was shown by peptidase digestion and immunoprecipitation with antibody to the NLS that v-Jun is phosphorylated at Ser248 in the cytoplasm but not in the nucleus. This phosphorylation is high in G1 and low in G2. Nuclear accumulation of v-Jun is correlated with underphosphorylation at Ser248. The regulation of nuclear import by phosphorylation was also examined using NLS peptides with Ser248 of v-Jun. Phosphorylation of the serine inhibited nuclear import mediated by the NLS peptide in vivo and in vitro. The protein kinase inhibitors staurosporine and H7 stimulated but the phosphatase inhibitor okadaic acid inhibited nuclear import mediated by the NLS peptide. The cytosolic activity of protein kinases phosphorylating Ser248 increased in G0 and decreased during cell cycle progression, reaching a minimum in G2, whereas phosphatase activity dephosphorylating Ser248 was not changed. These results show that nuclear import of v-Jun is negatively regulated by phosphorylation at Ser248 in the cytoplasm in a cell cycle-dependent manner.

scholarly journals YB-1 Phosphorylation at Serine 209 Inhibits Its Nuclear Translocation

2021 ◽  
Vol 23 (1) ◽  
pp. 428
Author(s):  
Ekaterina M. Sogorina ◽  
Ekaterina R. Kim ◽  
Alexey V. Sorokin ◽  
Dmitry N. Lyabin ◽  
Lev P. Ovchinnikov ◽  
...  
Keyword(s):  
Nuclear Localization ◽  
Posttranslational Modifications ◽  
Nuclear Import ◽  
Rna Binding ◽  
Nuclear Translocation ◽  
Dna And Rna ◽  
Localization Signal ◽  
And Migration ◽  
Dna And Rna Binding

YB-1 is a multifunctional DNA- and RNA-binding protein involved in cell proliferation, differentiation, and migration. YB-1 is a predominantly cytoplasmic protein that is transported to the nucleus in certain conditions, including DNA-damaging stress, transcription inhibition, and viral infection. In tumors, YB-1 nuclear localization correlates with high aggressiveness, multidrug resistance, and a poor prognosis. It is known that posttranslational modifications can regulate the nuclear translocation of YB-1. In particular, well-studied phosphorylation at serine 102 (S102) activates YB-1 nuclear import. Here, we report that Akt kinase phosphorylates YB-1 in vitro at serine 209 (S209), which is located in the vicinity of the YB-1 nuclear localization signal. Using phosphomimetic substitutions, we showed that S209 phosphorylation inhibits YB-1 nuclear translocation and prevents p-S102-mediated YB-1 nuclear import.

scholarly journals A Nonconventional Nuclear Localization Signal within the UL84 Protein of Human Cytomegalovirus Mediates Nuclear Import via the Importin α/β Pathway

2003 ◽  
Vol 77 (6) ◽  
pp. 3734-3748 ◽  
Author(s):  
Peter Lischka ◽  
Gabriele Sorg ◽  
Michael Kann ◽  
Michael Winkler ◽  
Thomas Stamminger
Keyword(s):  
Amino Acids ◽  
Dna Replication ◽  
Human Cytomegalovirus ◽  
Nuclear Localization ◽  
Nuclear Import ◽  
Nuclear Localization Signal ◽  
Complex Structure ◽  
Importin Α ◽  
Localization Signal

ABSTRACT The open reading frame UL84 of human cytomegalovirus encodes a multifunctional regulatory protein which is required for viral DNA replication and binds with high affinity to the immediate-early transactivator IE2-p86. Although the exact role of pUL84 in DNA replication is unknown, the nuclear localization of this protein is a prerequisite for this function. To investigate whether the activities of pUL84 are modulated by cellular proteins we used the Saccharomyces cerevisiae two-hybrid system to screen a cDNA-library for interacting proteins. Strong interactions were found between pUL84 and four members of the importin α protein family. These interactions could be confirmed in vitro by pull down experiments and in vivo by coimmunoprecipitation analysis from transfected cells. Using in vitro transport assays we showed that the pUL84 nuclear import required importin α, importin β, and Ran, thus following the classical importin-mediated import pathway. Deletion mutagenesis of pUL84 revealed a domain of 282 amino acids which is required for binding to the importin α proteins. Its function as a nuclear localization signal (NLS) was confirmed by fusion to heterologous proteins. Although containing a cluster of basic amino acids similar to classical NLSs, this cluster did not contain the NLS activity. Thus, a complex structure appears to be essential for importin α binding and import activity.

scholarly journals RanGTP Targets p97 to RanBP2, a Filamentous Protein Localized at the Cytoplasmic Periphery of the Nuclear Pore Complex

1997 ◽  
Vol 8 (12) ◽  
pp. 2379-2390 ◽  
Author(s):  
Christian Delphin ◽  
Tinglu Guan ◽  
Frauke Melchior ◽  
Larry Gerace
Keyword(s):  
Nuclear Localization ◽  
Nuclear Pore Complex ◽  
Nuclear Localization Signal ◽  
Protein Import ◽  
Critical Role ◽  
In Vitro Assays ◽  
Nuclear Pore ◽  
Localization Signal ◽  
Nuclear Localization Signal Receptor

RanBP2, a protein containing FG repeat motifs and four binding sites for the guanosine triphosphatase Ran, is localized at the cytoplasmic periphery of the nuclear pore complex (NPC) and is believed to play a critical role in nuclear protein import. We purified RanBP2 from rat liver nuclear envelopes and examined its structural and biochemical properties. Electron microscopy showed that RanBP2 forms a flexible filamentous molecule with a length of ∼36 nm, suggesting that it comprises a major portion of the cytoplasmic fibrils implicated in initial binding of import substrates to the NPC. Using in vitro assays, we characterized the ability of RanBP2 to bind p97, a cytosolic factor implicated in the association of the nuclear localization signal receptor with the NPC. We found that RanGTP promotes the binding of p97 to RanBP2, whereas it inhibits the binding of p97 to other FG repeat nucleoporins. These data suggest that RanGTP acts to specifically target p97 to RanBP2, where p97 may support the binding of an nuclear localization signal receptor/substrate complex to RanBP2 in an early step of nuclear import.

scholarly journals The importin-β binding domain of snurportin1 is responsible for the Ran- and energy-independent nuclear import of spliceosomal U snRNPs in vitro

2002 ◽  
Vol 156 (3) ◽  
pp. 467-479 ◽  
Author(s):  
Jochen Huber ◽  
Achim Dickmanns ◽  
Reinhard Lührmann
Keyword(s):  
Nuclear Import ◽  
Structural Similarity ◽  
Nuclear Pore ◽  
Independent Manner ◽  
Core Domain ◽  
U1 Snrnp ◽  
Importin Α ◽  
Localization Signal ◽  
Import Receptor

The nuclear localization signal (NLS) of spliceosomal U snRNPs is composed of the U snRNA's 2,2,7-trimethyl-guanosine (m3G)-cap and the Sm core domain. The m3G-cap is specifically bound by snurportin1, which contains an NH2-terminal importin-β binding (IBB) domain and a COOH-terminal m3G-cap–binding region that bears no structural similarity to known import adaptors like importin-α (impα). Here, we show that recombinant snurportin1 and importin-β (impβ) are not only necessary, but also sufficient for U1 snRNP transport to the nuclei of digitonin-permeabilized HeLa cells. In contrast to impα–dependent import, single rounds of U1 snRNP import, mediated by the nuclear import receptor complex snurportin1–impβ, did not require Ran and energy. The same Ran- and energy-independent import was even observed for U5 snRNP, which has a molecular weight of more than one million. Interestingly, in the presence of impβ and a snurportin1 mutant containing an impα IBB domain (IBBimpα), nuclear U1 snRNP import was Ran dependent. Furthermore, β-galactosidase (βGal) containing a snurportin1 IBB domain, but not IBBimpα-βGal, was imported into the nucleus in a Ran-independent manner. Our results suggest that the nature of the IBB domain modulates the strength and/or site of interaction of impβ with nucleoporins of the nuclear pore complex, and thus whether or not Ran is required to dissociate these interactions.

scholarly journals Importin-α Mediates the Regulated Nuclear Targeting of Serum- and Glucocorticoid-inducible Protein Kinase (Sgk) by Recognition of a Nuclear Localization Signal in the Kinase Central Domain

2003 ◽  
Vol 14 (3) ◽  
pp. 1221-1239 ◽  
Author(s):  
Anita C. Maiyar ◽  
Meredith L.L. Leong ◽  
Gary L. Firestone
Keyword(s):  
Protein Kinase ◽  
Nuclear Localization ◽  
Nuclear Import ◽  
Nuclear Localization Signal ◽  
Dependent Manner ◽  
Central Domain ◽  
Importin Α ◽  
Localization Signal ◽  
Inducible Protein

The transcriptionally regulated serum and glucocorticoid inducible protein kinase (Sgk) is localized to the nucleus in a serum-dependent manner, and a yeast two-hybrid genetic screen uncovered a specific interaction between Sgk and the importin-α nuclear import receptor. In vitro GST pull down assays demonstrated a strong and direct association of importin-α with endogenous Sgk and exogenously expressed HA-tagged Sgk, whereas both components coimmunoprecipitate and colocalize to the nucleus after serum stimulation. Consistent with an active mechanism of nuclear localization, the nuclear import of HA-Sgk in permeabilized cells required ATP, cytoplasm, and a functional nuclear pore complex. Ectopic addition of a 107 amino acid carboxy-terminal fragment of importin-α, which contains the Sgk binding region, competitively inhibited the ability of endogenous importin-α to import Sgk into nuclei in vitro. Mutagenesis of lysines by alanine substitution defined a KKAILKKKEEK sequence within the central domain of Sgk between amino acids 131–141 that functions as a nuclear localization signal (NLS) required for the in vitro interaction with importin-α and for nuclear import of full-length Sgk in cultured cells. The serum-induced nuclear import of Sgk requires the NLS-dependent recognition of Sgk by importin-α as well as the PI3-kinase–dependent phosphorylation of Sgk. Our results define a new role importin-α in the stimulus-dependent control of signal transduction by nuclear localized protein kinases.

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