SSB2/YNL209W Summary Help

Standard Name SSB2
Systematic Name YNL209W
Alias YG103 1
Feature Type ORF, Verified
Description Cytoplasmic ATPase that is a ribosome-associated molecular chaperone; functions with J-protein partner Zuo1p; may be involved in the folding of newly-synthesized polypeptide chains; member of the HSP70 family; SSB2 has a paralog, SSB1, that arose from the whole genome duplication (2, 3, 4, 5, 6 and see Summary Paragraph)
Name Description Stress-Seventy subfamily B
Chromosomal Location
ChrXIV:252059 to 253900 | ORF Map | GBrowse
Gene Ontology Annotations All SSB2 GO evidence and references
  View Computational GO annotations for SSB2
Molecular Function
Manually curated
Biological Process
Manually curated
Cellular Component
Manually curated
Regulators 11 genes
Classical genetics
Large-scale survey
2179 total interaction(s) for 2044 unique genes/features.
Physical Interactions
  • Affinity Capture-MS: 164
  • Affinity Capture-RNA: 1979
  • Affinity Capture-Western: 9
  • Co-fractionation: 3
  • PCA: 3
  • Reconstituted Complex: 2

Genetic Interactions
  • Dosage Lethality: 2
  • Dosage Rescue: 3
  • Phenotypic Enhancement: 3
  • Synthetic Growth Defect: 8
  • Synthetic Lethality: 1
  • Synthetic Rescue: 2

Expression Summary
Length (a.a.) 613
Molecular Weight (Da) 66,594
Isoelectric Point (pI) 5.24
Phosphorylation PhosphoGRID | PhosphoPep Database
sequence information
ChrXIV:252059 to 253900 | ORF Map | GBrowse
Last Update Coordinates: 2011-02-03 | Sequence: 1996-07-31
Subfeature details
Most Recent Updates
Coordinates Sequence
CDS 1..1842 252059..253900 2011-02-03 1996-07-31
Retrieve sequences
Analyze Sequence
S288C only
S288C vs. other species
S288C vs. other strains
External Links All Associated Seq | Entrez Gene | Entrez RefSeq Protein | MIPS | Search all NCBI (Entrez) | UniProtKB
Primary SGDIDS000005153

SSB1 and SSB2 encode chaperone proteins that are members of the S. cerevisiae SSB subfamily of cytosolic HSP70 proteins (1). HSP70 is a large family of proteins that has been evolutionarily conserved from bacteria (DnaK) to humans (HSP72/73). HSP70 proteins were originally classified based upon their induction by heat shock and their size of ~70kDa (reviewed in 7). S. cerevisiae has at least 9 cytosolic forms of HSP70 (SSA1, SSA2, SSA3, SSA4, SSB1, SSB2, SSE1, SSE2, SSZ1), 2 HSP70s which are found in the endoplasmic reticulum (KAR2, LHS1), and 3 mitochondrial HSP70 proteins (SSC1, SSQ1, ECM10). SSB1 and SSB2 are 99% identical to each other and 63% identical to SSA1-4, the main cytosolic subfamily of HSP70s (8). The main function of HSP70s is to serve as molecular chaperones, binding newly-translated proteins to assist in proper folding and prevent aggregation/misfolding (reviewed in 7 and 9). The chaperone activity of Ssb1p and Ssb2p is localized to the ribosome as part of the ribosome-associated complex (RAC; 10). RAC, which includes either Ssb1p or Ssb2p along with the Hsp70 protein Ssz1p and the DnaJ homolog Zuo1p, binds both the active ribosome and the associated nascent polypeptide chain (11).

Like all other Hsp70 proteins, Ssb1p and Ssb2p contain an N-terminal ATPase domain and a C-terminal peptide-binding domain (12). Unlike most HSP70 genes, SSB1 and SSB2 expression is repressed, as opposed to induced, upon heat shock (13). Instead, SSB transcription is coregulated with ribosomal protein genes (14). Double mutant strains null for both ssb1 and ssb2 are sensitive to cold and to translation-impairing drugs (13, 15). Overproduction of Ssb1p has been shown to cure cells propagating the prion form of Sup35p, [PSI+] (16, 17).

Last updated: 2006-02-07 Contact SGD

References cited on this page View Complete Literature Guide for SSB2
1) Werner-Washburne M, et al.  (1987) Complex interactions among members of an essential subfamily of hsp70 genes in Saccharomyces cerevisiae. Mol Cell Biol 7(7):2568-77
2) Craig EA, et al.  (1993) Heat shock proteins: molecular chaperones of protein biogenesis. Microbiol Rev 57(2):402-14
3) Lopez-Buesa P, et al.  (1998) The biochemical properties of the ATPase activity of a 70-kDa heat shock protein (Hsp70) are governed by the C-terminal domains. Proc Natl Acad Sci U S A 95(26):15253-8
4) Kim SY and Craig EA  (2005) Broad sensitivity of Saccharomyces cerevisiae lacking ribosome-associated chaperone ssb or zuo1 to cations, including aminoglycosides. Eukaryot Cell 4(1):82-9
5) Huang P, et al.  (2005) The Hsp70 Ssz1 modulates the function of the ribosome-associated J-protein Zuo1. Nat Struct Mol Biol 12(6):497-504
6) Byrne KP and Wolfe KH  (2005) The Yeast Gene Order Browser: combining curated homology and syntenic context reveals gene fate in polyploid species. Genome Res 15(10):1456-61
7) Bukau B and Horwich AL  (1998) The Hsp70 and Hsp60 chaperone machines. Cell 92(3):351-66
8) Boorstein WR, et al.  (1994) Molecular evolution of the HSP70 multigene family. J Mol Evol 38(1):1-17
9) Becker J and Craig EA  (1994) Heat-shock proteins as molecular chaperones. Eur J Biochem 219(1-2):11-23
10) Pfund C, et al.  (1998) The molecular chaperone Ssb from Saccharomyces cerevisiae is a component of the ribosome-nascent chain complex. EMBO J 17(14):3981-9
11) Gautschi M, et al.  (2002) A functional chaperone triad on the yeast ribosome. Proc Natl Acad Sci U S A 99(7):4209-14
12) Pfund C, et al.  (2001) Divergent functional properties of the ribosome-associated molecular chaperone Ssb compared with other Hsp70s. Mol Biol Cell 12(12):3773-82
13) Craig EA and Jacobsen K  (1985) Mutations in cognate genes of Saccharomyces cerevisiae hsp70 result in reduced growth rates at low temperatures. Mol Cell Biol 5(12):3517-24
14) Lopez N, et al.  (1999) SSB, encoding a ribosome-associated chaperone, is coordinately regulated with ribosomal protein genes. J Bacteriol 181(10):3136-43
15) Nelson RJ, et al.  (1992) The translation machinery and 70 kd heat shock protein cooperate in protein synthesis. Cell 71(1):97-105
16) Chacinska A, et al.  (2001) Ssb1 chaperone is a [PSI+] prion-curing factor. Curr Genet 39(2):62-7
17) Kushnirov VV, et al.  (2000) Chaperones that cure yeast artificial [PSI+] and their prion-specific effects. Curr Biol 10(22):1443-6