NopA64, a novel nucleolar phosphoprotein from proliferating onion cells, sharing immunological determinants with mammalian nucleolin |
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Authors: | Guillermo de Cárcer Antonio Cerdido Francisco Javier Medina |
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Institution: | (1) Centro de Investigaciones Biológicas (CSIC), Velázquez 144, E-28006 Madrid, Spain, ES |
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Abstract: | Five major soluble nuclear proteins associated with cell proliferation were identified in Allium cepa L. root cells. One of them, of 64 kDa, was revealed by Western blotting with anti-mammalian nucleolin antibodies. A polyclonal
antibody raised against this protein, which we have named NopA64, localised it in the nucleolus as well as in nuclear coiled
bodies. Together with NopA64, the antibody also revealed a smaller form, called NopA61. Both proteins were present in the
soluble ribonucleoprotein fraction and in the nuclear matrix of proliferating cells, but NopA61 was the only form revealed
in differentiated cells. NopA64 contained epitopes also present in other plants, in mammalian nucleolin and in its yeast homologue,
gar2. In mammals, the highest homology was with 50-kDa nucleolin fragments containing the RNA-binding motifs and the glycine-arginine-rich
(GAR) domain. NopA64 was moderately phosphorylated in vitro by exogenous casein kinase II and cdc2 kinase, whereas NopA61
was highly phosphorylated by casein kinase II. Furthermore, NopA61 was the only band detected after dephosphorylation as well
as after endoproteolysis of NopA64. This protein could be one of the various functional homologues of mammalian nucleolin
in plant cells.
Received: 2 July 1996 / Accepted: 15 October 1996 |
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Keywords: | :Allium Cell proliferation Nuclear protein Nucleolar protein Pre-rRNA processing Protein kinase |
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