Nuclear Accumulation of the U1 snRNP-Specific Protein C Is Due to Diffusion and Retention in the Nucleus

Gunnewiek, Jacqueline M. T. Klein; Aarssen, Yvonne van; Kemp, Annemiete van der; Nelissen, R.L.H.; Pruijn, Ger J. M.; Venrooij, W.J. van

doi:10.1006/excr.1997.3663

Cited by 8 publications

(6 citation statements)

References 38 publications

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“…Animal U1A protein was proposed to accumulate in the nucleus by an active, U1 snRNA independent mechanism [25], [39] whereas U1C protein accumulates in the nucleus by diffusion and nuclear retention [45]. However, neither of these two mechanisms could explain the behaviour of both U1A and U1C Arabidopsis proteins.…”

Section: Discussionmentioning

confidence: 99%

Role of Cajal Bodies and Nucleolus in the Maturation of the U1 snRNP in Arabidopsis

Lorković

Barta

2008

PLoS ONE

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BackgroundThe biogenesis of spliceosomal snRNPs takes place in both the cytoplasm where Sm core proteins are added and snRNAs are modified at the 5′ and 3′ termini and in the nucleus where snRNP-specific proteins associate. U1 snRNP consists of U1 snRNA, seven Sm proteins and three snRNP-specific proteins, U1-70K, U1A, and U1C. It has been shown previously that after import to the nucleus U2 and U4/U6 snRNP-specific proteins first appear in Cajal bodies (CB) and then in splicing speckles. In addition, in cells grown under normal conditions U2, U4, U5, and U6 snRNAs/snRNPs are abundant in CBs. Therefore, it has been proposed that the final assembly of these spliceosomal snRNPs takes place in this nuclear compartment. In contrast, U1 snRNA in both animal and plant cells has rarely been found in this nuclear compartment.Methodology/Principal FindingsHere, we analysed the subnuclear distribution of Arabidopsis U1 snRNP-specific proteins fused to GFP or mRFP in transiently transformed Arabidopsis protoplasts. Irrespective of the tag used, U1-70K was exclusively found in the nucleus, whereas U1A and U1C were equally distributed between the nucleus and the cytoplasm. In the nucleus all three proteins localised to CBs and nucleoli although to different extent. Interestingly, we also found that the appearance of the three proteins in nuclear speckles differ significantly. U1-70K was mostly found in speckles whereas U1A and U1C in ∼90% of cells showed diffuse nucleoplasmic in combination with CBs and nucleolar localisation.Conclusions/SignificanceOur data indicate that CBs and nucleolus are involved in the maturation of U1 snRNP. Differences in nuclear accumulation and distribution between U1-70K and U1A and U1C proteins may indicate that either U1-70K or U1A and U1C associate with, or is/are involved, in other nuclear processes apart from pre-mRNA splicing.

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Section: Discussionmentioning

confidence: 99%

Role of Cajal Bodies and Nucleolus in the Maturation of the U1 snRNP in Arabidopsis

Lorković

Barta

2008

PLoS ONE

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“…Although IκBα is sufficiently small to diffuse passively through the NPC, a recent report suggests that it is also imported by a piggy‐back mechanism through its association with an ankyrin repeat‐binding protein (Turpin et al ., 1999). The nuclear import of several small polypeptides such as histone H1 (Jakel et al ., 1999) and ribosomal proteins (Jakel and Gorlich, 1998) is carrier‐mediated, whereas rad24 (Lopez‐Girona et al ., 1999) and U1 snRNP‐specific protein C (Klein Gunnewiek et al ., 1997) localize to the nucleus by passive diffusion and subsequent retention in the nucleus.…”

Section: Discussionmentioning

confidence: 99%

A novel shuttling protein, 4E-T, mediates the nuclear import of the mRNA 5' cap-binding protein, eIF4E

et al. 2000

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The eukaryotic translation initiation factor 4E (eIF4E) plays an important role in the control of cell growth. eIF4E binds to the mRNA 5¢ cap structure m 7 GpppN (where N is any nucleotide), and promotes ribosome binding to the mRNA in the cytoplasm. However, a fraction of eIF4E localizes to the nucleus. Here we describe the cloning and functional characterization of a new eIF4E-binding protein, referred to as 4E-T (eIF4E-Transporter). We demonstrate that 4E-T is a nucleocytoplasmic shuttling protein that contains an eIF4E-binding site, one bipartite nuclear localization signal and two leucine-rich nuclear export signals. eIF4E forms a complex with the importin ab heterodimer only in the presence of 4E-T. Overexpression of wild-type 4E-T, but not of a mutant defective for eIF4E binding, causes the nuclear accumulation of HA-eIF4E in cells treated with leptomycin B. Taken together, these results demonstrate that the novel nucleocytoplasmic shuttling protein 4E-T mediates the nuclear import of eIF4E via the importin ab pathway by a piggy-back mechanism.

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“…However, there are a few reports of proteins which may enter the nucleus by diffusion. The free catalytic subunit of cAMP‐dependent protein kinase, snRNP protein U1C and a monomer of MAPK have been shown to localize to the nucleus after microinjection in cells cooled to 4 °C (40–42). These proteins depend upon associations with other nuclear proteins to remain in the nucleus.…”

Section: Discussionmentioning

confidence: 99%

“…Histone H1 and small cytoplasmic proteins containing an artificial NLS were shown to be localized to the nucleus by a receptor‐mediated process that excludes diffusion through the nuclear pores (39). Alternatively, the free catalytic subunit of cAMP‐dependent protein kinase, the U1 snRNP‐specific protein, U1C and a monomer of mitogen‐activated protein kinase have been shown by microinjection experiments to enter the nucleus by diffusion (40–42). In this report, we investigate the mechanism of nuclear import for the small nucleophilic protein, NHP6A, and show that it does not contain an identifiable NLS and enters the nucleus by a Ran‐independent nonclassical method.…”

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confidence: 91%

Nuclear Localization of the Saccharomyces cerevisiae HMG Protein NHP6A Occurs by a Ran‐Independent Nonclassical Pathway

Yen

Roberts

Johnson

2001

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The Saccharomyces cerevisiae non-histone protein 6-A (NHP6A) is a member of the high-mobility group 1/2 protein family that bind and bend DNA of mixed sequence. NHP6A has only one high-mobility group 1/2 DNA binding domain and also requires a 16-amino-acid basic tail at its N-terminus for DNA binding. We show in this report that nuclear accumulation of NHP6A is strictly correlated with its DNA binding properties since only nonhistone protein 6 A-green fluorescent protein chimeras that were competent for DNA binding were localized to the nucleus. Despite the requirement for basic residues within the N-terminal segment for DNA binding and nuclear accumulation, this region does not appear to contain a nuclear localization signal. Moreover, NHP6A does not bind to the yeast nuclear localization signal receptor SRP1 and nuclear targeting of NHP6A does not require the function of the 14 different importins. Unlike histone H2B1 which contains a classical nuclear localization signal, entry of NHP6A into the nucleus was found to be independent of Ran as judged by coexpression of Ran GTPase mutants and was shown to occur at 0 aeC after a 15-min induction. These unusual properties lead us to suggest that NHP6A entry into the nucleus proceeds by a nonclassical Ran-independent pathway. Key words: diffusion channel, green fluorescent protein, importins/karyopherins, nuclear import signals, nuclear pore complex, yeast Received 12 March 2001, revised and accepted for publication 24 April 2001Non-histone protein 6 A (NHP6A) is a homolog of the high mobility group 1/2 (HMG) family of proteins in Saccharomyces cerevisiae (1). The HMG1/2 class of proteins is defined by the HMG box, a DNA binding motif responsible for structure-specific or sequence-specific interactions (2,3). NHP6A is an 11-kDa protein that consists of a single 77-449 amino-acid HMG box that functions as a sequence-independent DNA binding domain (Figure 1). This region folds into the three a-helical L-shape characteristic of HMG1/2 proteins (4). In addition, NHP6A contains a 16-amino-acid segment N-terminal to the HMG box, which is unstructured in the absence of DNA. The N-terminal arm is highly basic and performs a critical function in mediating the relatively high-affinity DNA binding (5). The HMG box of NHP6A interacts with the minor groove of the DNA, while the N-terminal arm wraps around the DNA to make contacts with the phosphate backbone of the compressed major groove (4).NHP6A has been shown to function as a DNA architectural factor in specific recombination reactions such as Hin-catalyzed inversion and V(D)J gene assembly (6,7) as well as promote chromosome condensation in E. coli mutants lacking the major nucleoid-associated protein HU (7). Although the different roles of NHP6A in yeast have not been fully ascertained, NHP6A, along with its close homolog NHP6B, directly or indirectly modulates the expression of about 3% of yeast genes, including those transcribed by both RNA polymerase II and III (8-13). S. cerevisiae strains lacking NHP6A and NHP6B grow s...

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Nuclear Accumulation of the U1 snRNP-Specific Protein C Is Due to Diffusion and Retention in the Nucleus

Cited by 8 publications

References 38 publications

Role of Cajal Bodies and Nucleolus in the Maturation of the U1 snRNP in Arabidopsis

Role of Cajal Bodies and Nucleolus in the Maturation of the U1 snRNP in Arabidopsis

A novel shuttling protein, 4E-T, mediates the nuclear import of the mRNA 5' cap-binding protein, eIF4E

Nuclear Localization of the Saccharomyces cerevisiae HMG Protein NHP6A Occurs by a Ran‐Independent Nonclassical Pathway

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