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Snf5 is a core, non-ATPase subunit of the SWI/SNF chromatin-remodeling
complex that contributes to complex integrity and nucleosome engagement
rather than providing the catalytic ATPase activity, which in yeast is
carried by Snf2.
"Across yeast and metazoans, **Snf5/SMARCB1/INI1** is repeatedly framed as a **core subunit** that contributes to SWI/SNF complex integrity and nucleosome engagement rather than providing catalytic ATPase activity (which in yeast is carried by Snf2)."
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In budding-yeast SWI/SNF the nucleosome-binding lobe (NBL) is mainly
formed by Snf5, making Snf5 a principal nucleosome-contacting scaffold
within the complex.
"**Nucleosome-binding lobe (NBL)**: in budding-yeast SWI/SNF, the NBL is described as being **mainly formed by Snf5**, making Snf5 a principal nucleosome-contacting scaffold within the complex."
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The Snf5 finger helix is a C-terminal helix protruding from the NBL that
packs against the H2A-H2B surface and binds the nucleosome acidic patch
via multiple arginine residues.
"**Snf5 “finger helix” (FH)**: a C-terminal helix protruding from the NBL that **packs against the H2A–H2B surface** and binds the acidic patch via multiple arginine residues."
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Budding-yeast Snf5 largely composes the NBL and uses its finger helix to
bind the nucleosome H2A-H2B acidic patch through multiple arginine
residues; Arg669 is the canonical arginine anchor, equivalent to Arg370
in human SMARCB1.
"A key mechanistic advance synthesized in a 2023 review is that budding-yeast **Snf5 largely composes the NBL** and uses its **finger helix** to bind the nucleosome’s **H2A–H2B acidic patch** through **multiple arginine residues**."
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Mutations in the Snf5 finger helix reduce remodeling activity in vitro
and reduce fitness in vivo, linking the nucleosome-surface contact to
biologically relevant remodeling output.
"In the same framework, **mutations in the finger helix reduce remodeling activity in vitro and reduce fitness in vivo**, linking this nucleosome-surface contact to biologically relevant remodeling output."
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A 2024 review annotates Snf5 specifically as a proximal acidic-patch
binder within yeast SWI/SNF and places the complex's characteristic
activities as nucleosome sliding and histone ejection.
"A 2024 authoritative review further supports the assignment of **Snf5 as a “proximal acidic patch” binder** within yeast SWI/SNF and places SWI/SNF’s characteristic activities as **nucleosome sliding and histone ejection**."
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Snf5 can bind transcriptional activation domains (TADs); in
phospholipid biosynthetic gene regulation SWI/SNF subunits including
Snf5 bound Ino2 TADs, with discussion of interactions with other
activators such as Gcn4.
"In the context of phospholipid biosynthetic gene regulation, SWI/SNF subunits including **Snf5** were reported to bind **Ino2** TADs, and the study also discusses interactions with other activators such as **Gcn4**."
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Snf5 contributes to SWI/SNF transcriptional effects by acting as a
protein-protein interaction platform for activator-driven recruitment
and for coupling activator binding to remodeling.
"This supports a mechanistic view where Snf5 contributes to SWI/SNF’s transcriptional effects by acting as a **protein–protein interaction platform** for activator-driven recruitment and/or for coupling activator binding to remodeling."
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Recent yeast evidence shows Swi/Snf can directly repress transcription
in vivo through nucleosome remodeling, rather than repression being only
an indirect consequence of activation elsewhere.
"A major recent development in yeast is evidence that Swi/Snf can **directly repress transcription in vivo** through nucleosome remodeling, rather than repression being only an indirect consequence of activation elsewhere."
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Loss of Swi/Snf can paradoxically activate metabolic genes under
repressing conditions, especially sulfur metabolism (MET) genes,
producing a cysteine-deficient phenotype, correlating with global
redistribution of the transcription factor Met4.
"A 2023 *Nucleic Acids Research* study emphasizes that loss of Swi/Snf can paradoxically lead to **activation of metabolic genes under repressing conditions**, especially sulfur metabolism (MET) genes, and a **cysteine-deficient phenotype** despite growth in rich medium."
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Snf5 is a chromatin-associated factor by virtue of its role in SWI/SNF
remodeling of nucleosomes and direct nucleosome-surface (acidic patch)
binding; it is expected to be nuclear/chromatin-associated as a SWI/SNF
core subunit.
"Functionally, Snf5 is a chromatin-associated factor by virtue of its role in SWI/SNF remodeling of nucleosomes and direct nucleosome-surface binding (acidic patch)."