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Mol. Cell. Biol., 04 1997, 2235-2246, Vol 17, No. 4
E Noguchi, N Hayashi, N Nakashima and T Nishimoto
The Ran-GTPase cycle is important for nucleus-cytosol exchange of
macromolecules and other nuclear processes. We employed the two-hybrid
method to identify proteins interacting with Ran and the Ran GTP/GDP
exchange factor. Using PRP20, encoding the Ran GTP/GDP exchange factor, we
identified YRB1, previously identified as a protein able to interact with
human Ran GTP/GDP exchange factor RCC1 in the two-hybrid system. Using
GSP1, encoding the yeast Ran, as bait, we isolated YRB2. YRB2 encodes a
protein containing a Ran-binding motif similar to that found in Yrb1p and
Nup2p. Yrb1p is located in the cytosol whereas Nup2p is nuclear. Similar to
Yrb1p, Yrb2p bound to GTP-Gsp1p but not to GDP- Gsp1p and enhanced the
GTPase-activating activity of Rna1p. However, unlike Yrb1p, Yrb2p did not
inhibit the nucleotide-releasing activity of Prp20p. While overproduction
of Yrb1p inhibited the growth of a mutant possessing a PRP20 mutation
(srm1-1) and suppressed the rna1-1 mutation, overproduction of Yrb2p showed
no effect on the growth of these mutants. Disruption of YRB2 made yeast
cold sensitive and was synthetically lethal with rna1-1 but not with
nup2delta. Nuclear protein import and the mRNA export were normal in
strains possessing mutations of YRB2. We propose that Yrb2p is involved in
the nuclear processes of the Ran-GTPase cycle which are not related to
nucleus- cytosol exchange of macromolecules.
Copyright © 1997, American Society for Microbiology
Yrb2p, a Nup2p-related yeast protein, has a functional overlap with Rna1p, a yeast Ran-GTPase-activating protein
Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka, Japan.
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