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Systematic name YAL005C
Gene name SSA1
Aliases YG100
Feature type ORF, Verified
Coordinates Chr I:141431..139503
Primary SGDID S000000004

Description of YAL005C: ATPase involved in protein folding and NLS-directed nuclear transport; member of HSP70 family; forms chaperone complex with Ydj1p; localized to nucleus, cytoplasm, and cell wall; 98% identical with Ssa2p, but subtle differences between the two proteins provide functional specificity with respect to propagation of yeast [URE3] prions and vacuolar-mediated degradations of gluconeogenesis enzymes; general targeting factor of Hsp104p to prion fibrils[1][2][3][4][5][6][7]


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Physical interaction with FES1
Purified GST-Fes1p interacts with the ADP-bound form of (His6)-Ssa1p in GST pull down assays [8] [9]


YAL005C is regulated by cns1.Regulatory interaction with cns1
Cns1 exhibits no influence on the ATPase of Hsp90. However, it activates the ATPase of Ssa1 up to 30-fold by accelerating the rate-limiting ATP hydrolysis step. This stimulating effect is mediated by the N-terminal TPR-containing part of Cns1, whereas the C-terminal part showed no effect. [10] [11]

YAL005C is regulated by Sti1.Regulatory interaction with Sti1
Binding of Sti1 to Ssa1 activates the ATPase of Ssa1 by a factor of about 200, which is in contrast to the behaviour of Hop in the mammalian Hsp70 system. Analysis of the underlying activation mechanism revealed that ATP hydrolysis is rate limiting in the Ssa1 ATPase cycle and that this step is accelerated by Sti1. [12] [13]

Two Hybrid

Two Hybrid interaction with Sti1
With a two hybrid approach and coimmunoprecipitations, we show that Sti1 specifically interacts with the Ssa group of the cytosolic yeast Hsp70 proteins and not with the Ssb, Sse and Ssz group. [12] [13]



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  1. Bush GL and Meyer DI (1996) The refolding activity of the yeast heat shock proteins Ssa1 and Ssa2 defines their role in protein translocation. J Cell Biol 135(5):1229-37 SGD PMID 8947547
  2. Kim S, et al. (1998) Folding in vivo of a newly translated yeast cytosolic enzyme is mediated by the SSA class of cytosolic yeast Hsp70 proteins. Proc Natl Acad Sci U S A 95(22):12860-5 SGD PMID 9789005
  3. Lopez-Ribot JL and Chaffin WL (1996) Members of the Hsp70 family of proteins in the cell wall of Saccharomyces cerevisiae. J Bacteriol 178(15):4724-6 SGD PMID 8755907
  4. Sharma D and Masison DC (2011) Single methyl group determines prion propagation and protein degradation activities of yeast heat shock protein (Hsp)-70 chaperones Ssa1p and Ssa2p. Proc Natl Acad Sci U S A () SGD PMID 21808014
  5. Shulga N, et al. (1999) A nuclear export signal prevents Saccharomyces cerevisiae Hsp70 Ssb1p from stimulating nuclear localization signal-directed nuclear transport. J Biol Chem 274(23):16501-7 SGD PMID 10347213
  6. Winkler J, et al. (2012) Hsp70 targets Hsp100 chaperones to substrates for protein disaggregation and prion fragmentation. J Cell Biol 198(3):387-404 SGD PMID 22869599
  7. Ziegelhoffer T, et al. (1995) The dissociation of ATP from hsp70 of Saccharomyces cerevisiae is stimulated by both Ydj1p and peptide substrates. J Biol Chem 270(18):10412-9 SGD PMID 7737974
  8. Kabani M, et al. (2002) Nucleotide exchange factor for the yeast Hsp70 molecular chaperone Ssa1p. Mol Cell Biol 22(13):4677-89 SGD PMID 12052876
  9. submitted by Mehdi Kabani on 2003-03-31
  10. Hainzl O, et al. (2004) Cns1 is an activator of the Ssa1 ATPase activity. J Biol Chem 279(22):23267-73 SGD PMID 15044454
  11. submitted by Dr. Harald Wegele on 2004-07-15
  12. 12.0 12.1 Wegele H, et al. (2003) Sti1 is a novel activator of the Ssa proteins. J Biol Chem 278(28):25970-6 SGD PMID 12716905
  13. 13.0 13.1 submitted by Dr. Harald Wegele on 2003-09-03

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