Abstract 2500: Identification and characterization of a bipartite nuclear localization signal reveals non-canonical 'oncogenic' role for cytoplasm-restricted ARID1B

Mammalian Stau1 (Staufen1), a modular protein composed of several dsRBDs (double-stranded RNA-binding domains), is probably involved in mRNA localization. Although Stau1 is mostly described in association with the rough endoplasmic reticulum and ribosomes in the cytoplasm, recent studies suggest that it may transit through the nucleus/nucleolus. Using a sensitive yeast import assay, we show that Stau1 is actively imported into the nucleus through a newly identified bipartite nuclear localization signal. As in yeast, the bipartite nuclear localization signal is necessary for Stau1 nuclear import in mammalian cells. It is also required for Stau1 nucleolar trafficking. However, Stau1 nuclear transit seems to be regulated by mechanisms that involve cytoplasmic retention and/or facilitated nuclear export. Cytoplasmic retention is mainly achieved through the action of dsRBD3, with dsRBD2 playing a supporting role in this function. Similarly, dsRBD3, but not its RNA-binding activity, is critical for Stau1 nucleolar trafficking. The function of dsRBD3 is strengthened or stabilized by the presence of dsRBD4 but prevented by the interdomain between dsRBD2 and dsRBD3. Altogether, these results suggest that Stau1 nuclear trafficking is a highly regulated process involving several determinants. The presence of Stau1 in the nucleus/nucleolus suggests that it may be involved in ribonucleoprotein formation in the nucleus and/or in other nuclear functions not necessarily related to mRNA transport.

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Characterization of the Putative Transposase mRNA of Tag1, Which Is Ubiquitously Expressed in Arabidopsis and Can Be Induced by Agrobacterium-Mediated Transformation With dTag1 DNA

Genetics ◽

10.1093/genetics/149.2.693 ◽

1998 ◽

Vol 149 (2) ◽

pp. 693-701 ◽

Cited By ~ 3

Author(s):

Dong Liu ◽

Nigel M Crawford

Keyword(s):

Arabidopsis Thaliana ◽

Transposable Element ◽

Nuclear Localization ◽

Nuclear Localization Signal ◽

Transcript Levels ◽

Agrobacterium Mediated Transformation ◽

Transgenic Lines ◽

Localization Signal ◽

Transposase Mrna

Abstract Tag1 is an autonomous transposable element of Arabidopsis thaliana. Tag1 expression was examined in two ecotypes of Arabidopsis (Columbia and No-0) that were transformed with CaMV 35S-Tag1-GUS DNA. These ecotypes contain no endogenous Tag1 elements. A major 2.3-kb and several minor transcripts were detected in all major organs of the plants. The major transcript encoded a putative transposase of 84.2 kD with two nuclear localization signal sequences and a region conserved among transposases of the Ac or hAT family of elements. The abundance of Tag1 transcripts varied among transgenic lines and did not correlate with somatic excision frequency or germinal reversion rates, suggesting that factors other than transcript levels control Tag1 excision activity. In untransformed plants of the Landsberg ecotype, which contain two endogenous Tag1 elements, no Tag1 transcripts were detected. Agrobacterium-mediated transformation of these Landsberg plants with a defective 1.4-kb Tag1 element resulted in the appearance of full-length Tag1 transcripts from the endogenous elements. Transformation with control DNA containing no Tag1 sequences did not activate endogenous Tag1 expression. These results indicate that Agrobacterium-mediated transformation with dTag1 can activate the expression of Tag1.

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Hairless is translocated to the nucleus via a novel bipartite nuclear localization signal and is associated with the nuclear matrix

Journal of Cell Science ◽

10.1242/jcs.114.2.367 ◽

2001 ◽

Vol 114 (2) ◽

pp. 367-376

Author(s):

K. Djabali ◽

V.M. Aita ◽

A.M. Christiano

Keyword(s):

Amino Acid ◽

Hair Follicle ◽

Nuclear Localization ◽

Nuclear Matrix ◽

Nuclear Localization Signal ◽

Amino Acid Residues ◽

Bipartite Nuclear Localization Signal ◽

Hairless Gene ◽

Fractionation Analysis ◽

Localization Signal

Hair follicle cycling is an exquisitely regulated and dynamic process consisting of phases of growth, regression and quiescence. The transitions between the phases are governed by a growing number of regulatory proteins, including transcription factors. The hairless (hr) gene encodes a putative transcription factor that is highly expressed in the skin, where it appears to be an essential regulator during the regression of the catagen hair follicle. In hairless mice, as well as humans with congenital atrichia, the absence of hr gene function initiates a premature and abnormal catagen due to a dysregulation of apoptosis and cell adhesion, and defects in the signaling required for hair follicle remodeling. Here, we report structure-function studies of the hairless gene product, in which we identify a novel bipartite nuclear localization signal (NLS) of the form KRA(X13) PKR. Deletion analysis of the mouse hr gene mapped the NLS to amino acid residues 409–427. Indirect immunofluorescence microscopy of cells transiently transfected with hairless-green fluorescent fusion proteins demonstrated that these amino acid residues are necessary and sufficient for nuclear localization. Furthermore, nuclear fractionation analysis revealed that the hr protein is associated with components of the nuclear matrix.

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