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Gene Review

SSA4  -  Hsp70 family chaperone SSA4

Saccharomyces cerevisiae S288c

Synonyms: Heat shock protein SSA4, YER103W
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High impact information on SSA4

  • In situ hybridization indicated that heat-inducible SSA4 and SSA1 mRNAs were exported from nuclei under these same conditions [1].
  • Sequences within either the 5' 1600 or the 3' 500 nucleotides of SSA4 mRNA were sufficient to direct GAL1 mRNA to the cytoplasm during stress [1].
  • The export of SSA4 mRNA following stress required functional nuclear pore complexes, as SSA4 mRNA accumulated in nuclei following heat shock of cells containing temperature-sensitive nucleoporins [1].
  • We have characterized two heat shock mRNAs, SSA4 and HSP104, in these mutant backgrounds; each transcript concentrates in a single intranuclear focus [2].
  • The HSP12 promoter, with the highest level of histone displacement, showed the highest level of H3 acetylation, while the SSA4 promoter, with a lower histone displacement, showed only modest H3 acetylation [3].

Biological context of SSA4

  • Excess of Sfl1, Ssn8, and Rpp0 influenced at least one of the tested chaperone-specific promoters, SSA4, HSP104, and model promoters, with either the heat shock or stress response elements [4].
  • Overexpression of the STI1 gene resulted in substantial trans-activation of SSA4 promoter-reporter gene fusions, indicating that STI1 may play a role in mediating the heat shock response of some HSP70 genes [5].
  • The two genes encoding yeast ribosomal protein S8 reside on different chromosomes, and are closely linked to the hsp70 stress protein genes SSA3 and SSA4 [6].
  • When cell survival after heat shock at 50 or 56 degrees C was examined, our results showed that overexpression of SSA1 or SSA4 protein did not protect yeast cells against thermal stress, nor affect the cells' ability to develop thermotolerance [7].

Associations of SSA4 with chemical compounds

  • Third, the antibiotic thiolutin, previously demonstrated to inhibit all three yeast RNA polymerases both in vivo and in vitro, increases the RNA levels of HSP82 5- to 10-fold, those of SSA4 greater than 25-fold, and those of HSP26 greater than 50-fold under conditions in which transcription of non-heat-shock genes is blocked [8].

Other interactions of SSA4

  • In exa2-1 ssa1 ssa2 strains the gene products of the remaining SSA hsp70 genes, SSA3 and SSA4 (Ssa3/4p), accumulate to higher levels [9].
  • The SSA4 isoenzyme, which is produced only under stress conditions, has an uncoating activity intermediate between SSA1 and SSA2 [10].
  • The ability to drive basal transcription is not inherent in all natural HSEs, since the HSEs from the heat-inducible SSA3 and SSA4 genes showed no basal activity when placed in the CYC1 vector [11].
  • Uncapped poly(A)+ SSA4 mRNA accumulated in cells lacking the 5' exoribonuclease Xrn1 [12].


  1. Regulation of mRNA export in response to stress in Saccharomyces cerevisiae. Saavedra, C., Tung, K.S., Amberg, D.C., Hopper, A.K., Cole, C.N. Genes Dev. (1996) [Pubmed]
  2. A block to mRNA nuclear export in S. cerevisiae leads to hyperadenylation of transcripts that accumulate at the site of transcription. Jensen, T.H., Patricio, K., McCarthy, T., Rosbash, M. Mol. Cell (2001) [Pubmed]
  3. Displacement of Histones at Promoters of Saccharomyces cerevisiae Heat Shock Genes Is Differentially Associated with Histone H3 Acetylation. Erkina, T.Y., Erkine, A.M. Mol. Cell. Biol. (2006) [Pubmed]
  4. Increased expression of Hsp40 chaperones, transcriptional factors, and ribosomal protein Rpp0 can cure yeast prions. Kryndushkin, D.S., Smirnov, V.N., Ter-Avanesyan, M.D., Kushnirov, V.V. J. Biol. Chem. (2002) [Pubmed]
  5. Isolation and characterization of STI1, a stress-inducible gene from Saccharomyces cerevisiae. Nicolet, C.M., Craig, E.A. Mol. Cell. Biol. (1989) [Pubmed]
  6. The two genes encoding yeast ribosomal protein S8 reside on different chromosomes, and are closely linked to the hsp70 stress protein genes SSA3 and SSA4. Logghe, M., Molemans, F., Fiers, W., Contreras, R. Yeast (1994) [Pubmed]
  7. Thermal response of yeast cells overexpressing hsp70 genes. Weitzel, G., Li, G.C. International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group. (1993) [Pubmed]
  8. The yeast heat shock response is induced by conversion of cells to spheroplasts and by potent transcriptional inhibitors. Adams, C.C., Gross, D.S. J. Bacteriol. (1991) [Pubmed]
  9. Isolation and characterization of extragenic suppressors of mutations in the SSA hsp70 genes of Saccharomyces cerevisiae. Nelson, R.J., Heschl, M.F., Craig, E.A. Genetics (1992) [Pubmed]
  10. Uncoating of coated vesicles by yeast hsp70 proteins. Gao, B.C., Biosca, J., Craig, E.A., Greene, L.E., Eisenberg, E. J. Biol. Chem. (1991) [Pubmed]
  11. Saccharomyces cerevisiae HSP70 heat shock elements are functionally distinct. Young, M.R., Craig, E.A. Mol. Cell. Biol. (1993) [Pubmed]
  12. Accelerated mRNA decay in conditional mutants of yeast mRNA capping enzyme. Schwer, B., Mao, X., Shuman, S. Nucleic Acids Res. (1998) [Pubmed]
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