Annotation inferences using phylogenetic trees
Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
Electronic Gene Ontology annotations created by ARBA machine learning models
Combined Automated Annotation using Multiple IEA Methods
Subcellular localization of the yeast proteome.
The translation machinery and 70 kd heat shock protein cooperate in protein synthesis.
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The SSB Hsp70s (Ssb1/2p) are associated with translating ribosomes, an
association disrupted by puromycin, suggesting Ssb binds directly to the
nascent polypeptide chain.
"The SSB hsp70s (Ssb1/2p) are associated with translating ribosomes. This association is disrupted by puromycin, suggesting that Ssb1/2p may bind directly to the nascent polypeptide."
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Mutant ssb1 ssb2 strains grow slowly, contain fewer translating ribosomes,
and are hypersensitive to protein synthesis inhibitors.
"Mutant ssb1 ssb2 strains grow slowly, contain a low number of translating ribosomes, and are hypersensitive to several inhibitors of protein synthesis."
The ribosome-bound chaperones RAC and Ssb1/2p are required for accurate translation in Saccharomyces cerevisiae.
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Translational fidelity is impaired in the absence of functional RAC or
Ssb1/2p, with the principal defect in translation termination.
"Translational fidelity was impaired in the absence of functional RAC or Ssb1/2p, and the effect was further enhanced by paromomycin. The mutant strains suffered primarily from a defect in translation termination"
Proteome survey reveals modularity of the yeast cell machinery.
Global landscape of protein complexes in the yeast Saccharomyces cerevisiae.
Specific effects of ribosome-tethered molecular chaperones on programmed -1 ribosomal frameshifting.
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Deletion of Ssb1p/Ssb2p or of Ssz1p/Zuo1p (RAC) specifically inhibits -1
programmed ribosomal frameshifting and impairs Killer virus maintenance,
with no effect on +1 PRF.
"deletion of Ssb1p/Ssb2p or of Ssz1p/Zuo1p resulted in specific inhibition of -1 PRF and defects in Killer virus maintenance, while no effects were observed on +1 PRF."
The plasma membrane proteome of Saccharomyces cerevisiae and its response to the antifungal calcofluor.
An atlas of chaperone-protein interactions in Saccharomyces cerevisiae: implications to protein folding pathways in the cell.
The Hsp70 homolog Ssb is essential for glucose sensing via the SNF1 kinase network.
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The chaperone Ssb is required to keep SNF1 in the nonphosphorylated state in
the presence of glucose; Deltassb1 Deltassb2 cells display features
reminiscent of glucose-repression mutants.
"the chaperone Ssb is required to keep SNF1 in the nonphosphorylated state in the presence of glucose."
A ribosome-anchored chaperone network that facilitates eukaryotic ribosome biogenesis.
The cotranslational function of ribosome-associated Hsp70 in eukaryotic protein homeostasis.
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The yeast Hsp70 SSB binds a subset of nascent polypeptides whose intrinsic
properties and slow translation rates hinder cotranslational folding; the
SSB-ribosome cycle and substrate recognition are modulated by RAC.
"SSB binds to a subset of nascent polypeptides whose intrinsic properties and slow translation rates hinder efficient cotranslational folding. The SSB-ribosome cycle and substrate recognition is modulated by its ribosome-bound cochaperone, RAC."
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Deletion of SSB leads to widespread aggregation of newly synthesized
polypeptides, demonstrating its proteome-wide cotranslational folding role.
"Deletion of SSB leads to widespread aggregation of newly synthesized polypeptides."
ATPase-Modulated Stress Granules Contain a Diverse Proteome and Substructure.
RNA-dependent interactome allows network-based assignment of RNA-binding protein function.
The social and structural architecture of the yeast protein interactome.
The molecular chaperone Ssb from Saccharomyces cerevisiae is a component of the ribosome-nascent chain complex.
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Ssb can be cross-linked to nascent chains and is released together with
nascent chains upon puromycin treatment, demonstrating direct interaction
with the nascent polypeptide.
"Ssb could be cross-linked to nascent chains containing a modified lysine residue with a photoactivatable cross-linker."
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Ssb is a core component of the translating ribosome that interacts with both
the nascent chain and the ribosome, functioning as a chaperone that prevents
misfolding of newly synthesized proteins.
"Ssb is a core component of the translating ribosome which interacts with both the nascent polypeptide chain and the ribosome. These interactions allow Ssb to function as a chaperone on the ribosome, preventing the misfolding of newly synthesized proteins."
The biochemical properties of the ATPase activity of a 70-kDa heat shock protein (Hsp70) are governed by the C-terminal domains.
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Ssb has an unusually low steady-state affinity for ATP but a higher maximal
velocity, and its ATPase (unlike Ssa) is K+-independent; the peptide-binding
domain shapes these properties.
"Ssb, however, has an unusually low steady-state affinity for ATP but a higher maximal velocity. In addition, the ATPase activity of Hsp70s, like that of Ssa1, depends on the addition of K+ whereas Ssb activity does not."
Falcon deep research report on SSB2 (yeast, UniProt P40150 / YNL209W)
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SSB2 (P40150/YNL209W) is one of two nearly identical ribosome-associated
cytosolic Hsp70s in S. cerevisiae; SSB1 and SSB2 differ by ~4 residues and
are generally studied together as "Ssb", confirming this is the genuine
Ssb-type Hsp70 (not an unrelated same-symbol gene).
"Ssb is encoded by **two paralogous genes, SSB1 and SSB2**"
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Ssb2 is a canonical Hsp70 with an N-terminal ATPase/nucleotide-binding
domain (NBD) and a C-terminal substrate-binding domain (SBD), driven by an
ATP-dependent conformational cycle.
"core biochemistry is an **ATP-driven conformational cycle**"
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The RAC J-domain protein Zuo1 stimulates Ssb1/2 ATP hydrolysis, driving the
high-affinity substrate state that stabilizes nascent-chain binding.
"J-domain protein **Zuo1** stimulates ATP hydrolysis of **Ssb1/2**, driving this high-affinity substrate engagement on nascent chains"
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Ssb belongs to an Hsp70 triad at the ribosomal tunnel exit (RAC = Zuo1 +
Ssz1, plus Ssb), with RAC recruiting and activating Ssb to directly bind
nascent chains for cotranslational folding.
"Ssb2 belongs to an **Hsp70 triad at the exit tunnel**"
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Ssb1/2 are the direct nascent-chain binders during cotranslational folding
in yeast; RAC is an obligate Zuo1-Ssz1 heterodimer anchored to the ribosome
via Zuo1.
"RAC is an obligate Zuo1–Ssz1 heterodimer attached to the ribosome (via Zuo1)"
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Ssb is cytosolic and ribosome-associated at the 60S tunnel exit; about 50%
of total cellular Ssb is ribosome-bound at steady state (~1:1 with
ribosomes), with the remainder free cytosolic.
"only about **~50% of total cellular Ssb** is ribosome-associated at steady state"
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Ssb's cotranslational substrate coverage is broad, engaging ~80% of
cytosolic/nuclear nascent proteins, supporting a proteome-wide
cotranslational folding role.
"Ssb’s co-translational substrate coverage is broad"
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Single SSB1 or SSB2 deletion gives little phenotype owing to redundancy,
whereas combined ssb1/2 deletion causes broad defects.
"Single-gene loss has little obvious phenotype, whereas combined **ssb1/2Δ** causes broad defects"
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Ssb suppresses formation and/or inheritance of multiple amyloid/prion-like
heritable elements, linking it to proteostasis and aggregation control.
"Ssb suppresses formation and/or inheritance of multiple **amyloid/prion-like elements**"
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The RAC/Ssb system is required for proper translational downregulation and
proteostasis during TORC1 inhibition, connecting tunnel-exit chaperoning to
nutrient/stress signaling.
"RAC/Ssb system is required for proper translational downregulation and proteostasis during TORC1 inhibition"
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Ssb/RAC is linked to recruitment of the ubiquitin ligase Ltn1, connecting
cotranslational chaperoning to ribosome-associated quality control.
"Ssb/RAC is linked to recruitment of the ubiquitin ligase **Ltn1**"
OpenScientist hypothesis investigation - shared SSB1/SSB2 cotranslational folding versus paralog specialization
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The investigation supports shared cotranslational chaperoning and finds no demonstrated paralog-specific substrate or mechanistic distinction. It does not investigate protein refolding.
"absence of evidence for divergence is not the same as proof of perfect functional identity"
Current PANTHER PTHR19375 PAINT annotation snapshot