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Nuclear import of the U1A splicesome protein is mediated by importin alpha /beta and Ran in living mammalian cells. 2001

M Hieda, and T Tachibana, and M Fukumoto, and Y Yoneda
Department of Cell Biology and Neuroscience, Graduate School of Medicine, Osaka University, 2-2 Yamada-oka and Institute for Molecular and Cellular Biology, Osaka University, 1-3 Yamada-oka, Suita, Osaka 565-0871, Japan.

U1A is a component of the uracil-rich small nuclear ribonucleoprotein. The molecular mechanism of nuclear import of U1A was investigated in vivo and in vitro. When recombinant deletion mutants of U1A are injected into the BHK21 cell cytoplasm, the nuclear localization signal (NLS) of U1A is found in the N-terminal half of the central domain (residues 100-144 in mouse U1A). In an in vitro assay, it was found that the U1A-NLS accumulated in only a portion of the nuclei in the absence of cytosolic extract. In contrast, the addition of importin alpha/beta and Ran induced the uniform nuclear accumulation of U1A-NLS in all cells. Furthermore, U1A was found to bind the C-terminal portion of importin alpha. In addition, the in vitro nuclear migration of full-length U1A was found to be exclusively dependent on importin alpha/beta and Ran. Moreover, in living cells, the full-length U1A accumulated in the nucleus in a Ran-dependent manner, and nuclear accumulation was inhibited by the importin beta binding domain of importin alpha. These results suggest that the nuclear import of U1A is mediated by at least two distinct pathways, an importin alpha/beta and Ran-dependent and an -independent pathway in permeabilized cells, and that the latter pathway may be suppressed in intact cells.

UI MeSH Term Description Entries
D008164 Luminescent Proteins Proteins which are involved in the phenomenon of light emission in living systems. Included are the "enzymatic" and "non-enzymatic" types of system with or without the presence of oxygen or co-factors. Bioluminescent Protein,Bioluminescent Proteins,Luminescent Protein,Photoprotein,Photoproteins,Protein, Bioluminescent,Protein, Luminescent,Proteins, Bioluminescent,Proteins, Luminescent
D008322 Mammals Warm-blooded vertebrate animals belonging to the class Mammalia, including all that possess hair and suckle their young. Mammalia,Mammal
D008969 Molecular Sequence Data Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories. Sequence Data, Molecular,Molecular Sequencing Data,Data, Molecular Sequence,Data, Molecular Sequencing,Sequencing Data, Molecular
D009687 Nuclear Proteins Proteins found in the nucleus of a cell. Do not confuse with NUCLEOPROTEINS which are proteins conjugated with nucleic acids, that are not necessarily present in the nucleus. Nucleolar Protein,Nucleolar Proteins,Nuclear Protein,Protein, Nuclear,Protein, Nucleolar,Proteins, Nuclear,Proteins, Nucleolar
D011994 Recombinant Proteins Proteins prepared by recombinant DNA technology. Biosynthetic Protein,Biosynthetic Proteins,DNA Recombinant Proteins,Recombinant Protein,Proteins, Biosynthetic,Proteins, Recombinant DNA,DNA Proteins, Recombinant,Protein, Biosynthetic,Protein, Recombinant,Proteins, DNA Recombinant,Proteins, Recombinant,Recombinant DNA Proteins,Recombinant Proteins, DNA
D002286 Carcinoma, Ehrlich Tumor A transplantable, poorly differentiated malignant tumor which appeared originally as a spontaneous breast carcinoma in a mouse. It grows in both solid and ascitic forms. Ehrlich Ascites Tumor,Ascites Tumor, Ehrlich,Ehrlich Tumor Carcinoma,Tumor, Ehrlich Ascites
D002460 Cell Line Established cell cultures that have the potential to propagate indefinitely. Cell Lines,Line, Cell,Lines, Cell
D002467 Cell Nucleus Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (CELL NUCLEOLUS). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the ENDOPLASMIC RETICULUM. A cell may contain more than one nucleus. (From Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed) Cell Nuclei,Nuclei, Cell,Nucleus, Cell
D002474 Cell-Free System A fractionated cell extract that maintains a biological function. A subcellular fraction isolated by ultracentrifugation or other separation techniques must first be isolated so that a process can be studied free from all of the complex side reactions that occur in a cell. The cell-free system is therefore widely used in cell biology. (From Alberts et al., Molecular Biology of the Cell, 2d ed, p166) Cellfree System,Cell Free System,Cell-Free Systems,Cellfree Systems,System, Cell-Free,System, Cellfree,Systems, Cell-Free,Systems, Cellfree
D003593 Cytoplasm The part of a cell that contains the CYTOSOL and small structures excluding the CELL NUCLEUS; MITOCHONDRIA; and large VACUOLES. (Glick, Glossary of Biochemistry and Molecular Biology, 1990) Protoplasm,Cytoplasms,Protoplasms

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