Role of Nuclear Trafficking in Regulating Cellular Activity

Feldherr, Carl M.; Akin, Debra

doi:10.1016/s0074-7696(08)62633-9

Cited by 35 publications

(13 citation statements)

References 195 publications

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“…Rates of nuclear import vary depending on physiological conditions (Feldherr and Akin, 1994). According to either model presented above, the relative rates of nuclear import could be limited directly by the concentration of RanGAP1 at the NPC.…”

Section: Discussionmentioning

confidence: 99%

A novel ubiquitin-like modification modulates the partitioning of the Ran-GTPase-activating protein RanGAP1 between the cytosol and the nuclear pore complex.

Matunis

Coutavas

Blobel

1996

The Journal of Cell Biology

1,076

973

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Abstract. Ran is a nuclear Ras-like GTPase that is required for the bidirectional transport of proteins and ribonucleoproteins across the nuclear pore complex (NPC). A key regulator of the Ran GTP/GDP cycle is the 70:kD Ran-GTPase-activating protein RanGAP1. Here, we report the identification and localization of a novel form of RanGAP1. Using peptide sequence analysis and specific mAbs, RanGAP1 was found to be modified by conjugation to a ubiquitin-like protein.Immunoblot analysis and immunolocalization by light and EM demonstrated that the 70-kD unmodified form of RanGAP1 is exclusively cytoplasmic, whereas the 90-kD modified form of RanGAP1 is associated with the cytoplasmic fibers of the NPC. The modified form of RanGAP1 also appeared to associate with the mitotic spindle apparatus during mitosis. These findings have specific implications for Ran function and broad implications for protein regulation by ubiquitin-like modifications. Moreover, the variety and function of ubiquitin-like protein modifications in the cell may be more diverse than previously realized.T RANSPORT of macromolecules across the nuclear envelope occurs bidirectionally through nuclear pore complexes (NPCs) 1, large supramolecular assemblies that span both membranes of the nuclear envelope (Rout and Wente, 1994). Whereas small ions and metabolites can passively diffuse through the NPC, most proteins and ribonucleoproteins are transported across the NPC by a signal-and energy-dependent mechanism. Dissection of the events culminating in nuclear import has been aided by the development of a permeabilized cell system that has made possible the identification of soluble cytosolic factors required for nuclear import (Adam et al., 1990), and more recently by the development of solution binding assays that use recombinant transport factors and nucleoporins .Using the permeabilized cell assay in conjunction with biochemical fractionation of cytosolic extracts, four factors required for nuclear import have been purified and characterized (Moore and

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Section: Discussionmentioning

confidence: 99%

A novel ubiquitin-like modification modulates the partitioning of the Ran-GTPase-activating protein RanGAP1 between the cytosol and the nuclear pore complex.

Matunis

Coutavas

Blobel

1996

The Journal of Cell Biology

1,076

973

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“…For example, proliferating cells import faster and have a larger apparent active NPC diameter than do quiescent cells (253). Similar differences are seen between transformed and nontransformed cells or between cells immediately after mitosis and at later times in the cell cycle (252). Although the molecular basis of these effects is still unknown, it is hard to see how they could be explained without proposing changes in the NPC itself.…”

Section: Regulation Of Nucleocytoplasmic Transportmentioning

confidence: 99%

NUCLEOCYTOPLASMIC TRANSPORT: The Soluble Phase

Mattaj

Englmeier

1998

Annu. Rev. Biochem.

1,108

993

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Active transport between the nucleus and cytoplasm involves primarily three classes of macromolecules: substrates, adaptors, and receptors. Some transport substrates bind directly to an import or an export receptor while others require one or more adaptors to mediate formation of a receptor-substrate complex. Once assembled, these transport complexes are transferred in one direction across the nuclear envelope through aqueous channels that are part of the nuclear pore complexes (NPCs). Dissociation of the transport complex must then take place, and both adaptors and receptors must be recycled through the NPC to allow another round of transport to occur. Directionality of either import or export therefore depends on association between a substrate and its receptor on one side of the nuclear envelope and dissociation on the other. The Ran GTPase is critical in generating this asymmetry. Regulation of nucleocytoplasmic transport generally involves specific inhibition of the formation of a transport complex; however, more global forms of regulation also occur. CONTENTS

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“…This raises the question as to the mechanism by which homocitrate synthase is transported to the nucleus. The 47-kDa size of Lys20p is near the upper limit for diffusion across the nuclear pore complex, but could readily accumulate in the nucleus if bound to a nuclear component (21). Alternatively, nuclear transport of Lys20p may be explained either by "piggyback" transport in association with a nuclear protein, or the presence of an atyp- ical NLS.…”

Section: Lys20 and Ydl131w Gene Products Expressed In E Coli-mentioning

confidence: 99%

Homocitrate Synthase Is Located in the Nucleus in the YeastSaccharomyces cerevisiae

Chen

Brockenbrough

Dove

et al. 1997

Journal of Biological Chemistry

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We have generated monoclonal antibodies against nuclear proteins from the yeast Saccharomyces cerevisiae. The monoclonal antibodies react with proteins of 47 and 49 kDa on immunoblots and with partially overlapping sets of proteins on two-dimensional nonequilibrium pH gradient electrophoresis-SDS blots. Immunofluorescence localization shows a nuclear staining pattern. Immunoscreening a yeast expression library yielded five independent full-length clones of two open reading frames from chromosome IV, corresponding to YDL182w (LYS20) and YDL131w in the Saccharomyces genome data base. These two open reading frames are predicted to encode homocitrate synthase isozymes of 47 and 49 kDa, respectively. A clone carrying YDL182w was sequenced in its entirety and directs the expression of a 47-kDa protein in Escherichia coli. A clone carrying YDL131w expresses a 49-kDa protein in E. coli. Yeast grown in minimal medium plus lysine show significant reductions in nuclear immunofluorescence staining. Cell fractionation studies localize the 47-and 49-kDa proteins to the nucleus. Nuclear fractionation studies reveal that a portion of the 47-and 49-kDa proteins can only be extracted with DNase digestion and high salt. The localization of homocitrate synthase to the nucleus is unexpected given previous reports that homocitrate synthase is present in mitochondria and the cytoplasm in S. cerevisiae.In yeast, higher fungi, and euglenids, lysine is synthesized via the ␣-aminoadipate pathway, which is only found in these organisms (1). Homocitrate synthase catalyzes the first committed reaction in this pathway and is thought to be an important site of control of metabolic flow. In Saccharomyces cerevisiae, two isozymes have been identified by isoelectric focusing of purified enzyme preparations (2). Both isozymes are feedback inhibited by lysine, but only one is transcriptionally repressed by lysine (2).Genes for the homocitrate synthase isozymes have not been identified until recently, despite extensive genetic analyses of lysine auxotrophs, which have revealed most of the enzymeencoding (LYS) genes required in this pathway. During the sequencing of chromosome IV of S. cerevisiae, an open reading frame (ORF) 1 was identified that encoded a protein with significant homology to homocitrate synthase from other yeasts (3). This ORF is designated YDL182w in the Saccharomyces genome data base (GenBank™ accession number X83276, ORF D1298). Ramos et al. (4) have disrupted this gene, examined the effects on lysine production and levels of homocitrate synthase enzymatic activity, and named this gene LYS20. The subcellular localization of enzymes of the ␣-aminoadipate pathway has been investigated in S. cerevisiae, and the enzymes for the first half of the pathway have been reported to be located in the mitochondrion (reviewed in Ref. 5). Two reports place homocitrate synthase from S. cerevisiae in mitochondria (6, 7). Jaklitsch and Kubicek (8) reported that homocitrate synthase from Penicillium chrysogenum is present in the mitochondrion and ...

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Role of Nuclear Trafficking in Regulating Cellular Activity

Cited by 35 publications

References 195 publications

A novel ubiquitin-like modification modulates the partitioning of the Ran-GTPase-activating protein RanGAP1 between the cytosol and the nuclear pore complex.

A novel ubiquitin-like modification modulates the partitioning of the Ran-GTPase-activating protein RanGAP1 between the cytosol and the nuclear pore complex.

NUCLEOCYTOPLASMIC TRANSPORT: The Soluble Phase

Homocitrate Synthase Is Located in the Nucleus in the YeastSaccharomyces cerevisiae

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