The carrier Msn5p/Kap142p promotes nuclear export of the hsp70 Ssa4p and relocates in response to stress.
Cytoplasmic hsp70s like yeast Ssa4p shuttle between nucleus and cytoplasm under normal growth conditions but accumulate in nuclei upon stress. This nuclear accumulation is only transient, and Ssa4p relocates to the cytoplasm when cells recover. We show here that Ssa4p nuclear export is independent of Xpol/Crm1 and identify the importin-beta family member Msn5p/Kap142p as the exporter for Ssa4p. In growing cells and in vitro, Msn5p and Ssa4p generate genuine export complexes that require Ran/Gsp1p-GTP. Furthermore, nucleoporin Nup82p, which plays a role in Msn5p-mediated transport, is necessary for efficient export of Ssa4p. In living cells, stress not only regulates Ssa4p localization, but also controls the distribution of Msn5p. Msn5p is concentrated in nuclei of unstressed cells, but appears in the cytoplasm upon exposure to ethanol, heat, starvation or severe oxidative stress. In addition, growth on non-fermentable carbon sources relocates a portion of Msn5p to the cytoplasm and leads to a partial nuclear accumulation of Ssa4p. Taken together, growth and stress conditions that localize the transporter Msn5p to the cytoplasm also induce the nuclear accumulation of its cargo Ssa4p.
Quan
XinXin
X
Department of Physiology, McGill University, 3655 Promenade Sir William Osler, Montreal, QC, H3G 1Y6, Canada.
Tsoulos
Panagiotis
P
Kuritzky
Alexandra
A
Zhang
Rui
R
Stochaj
Ursula
U
D021581:Active Transport, Cell Nucleus / Q000502:physiology; D015153:Blotting, Western; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D000431:Ethanol / Q000633:toxicity; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006358:Hot Temperature; D006861:Hydrogen Peroxide / Q000633:toxicity; D047468:Immunoprecipitation; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D009154:Mutation / Q000235:genetics; D028861:Nuclear Pore Complex Proteins / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D013997:Time Factors; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
D018840:HSP70 Heat-Shock Proteins; D028884:Karyopherins; C401306:MSN5 protein, S cerevisiae; D028861:Nuclear Pore Complex Proteins; D011993:Recombinant Fusion Proteins; C456269:SSA4 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D000431:Ethanol; D006861:Hydrogen Peroxide; D001616:beta-Galactosidase