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Updated: May 13, 2026
10:14
Biochemical Assays for Analyzing Activities of ATP-dependent Chromatin Remodeling Enzymes
Published on: October 25, 2014
Evidence for monomeric actin function in INO80 chromatin remodeling
Prabodh Kapoor1, Mingming Chen, Duane David Winkler
1Department of Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Smithville, Texas, USA.
Nature Structural & Molecular Biology
|March 26, 2013
Summary
Nuclear actin monomers, distinct from cytoplasmic actin, are essential for the INO80 chromatin remodeling complex. A specific actin mutation impairs nuclear functions and chromatin remodeling activity.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Actin's primary functions are well-documented in the cytoplasm.
- The specific roles of actin within the cell nucleus are less understood.
Purpose of the Study:
- To investigate the function of nuclear actin within the INO80 chromatin remodeling complex.
- To elucidate the mechanism of nuclear actin's involvement in chromatin remodeling.
Main Methods:
- Genetic analysis of yeast strains with specific actin mutations.
- Biochemical assays to assess chromatin remodeling activity in vitro.
- Studying the INO80 complex, a nuclear actin-containing complex.
Main Results:
- Nuclear actin functions as a monomer within the INO80 complex.
- The barbed end of nuclear actin is inaccessible for polymerization.
- An actin mutation in subdomain 2 impairs in vivo nuclear functions and reduces INO80 chromatin remodeling activity.
- Subdomain 2 of actin is crucial for INO80's interaction with chromatin.
Conclusions:
- Nuclear actin has an evolutionarily conserved function in its monomeric form.
- Nuclear actin employs a distinct mechanism compared to cytoplasmic actin.
- Monomeric nuclear actin plays a critical role in chromatin remodeling via the INO80 complex.
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Arp2/3 Complex
Arp2/3 complex is a seven-subunit complex consisting of two proteins similar to actin- Arp2 and Arp3, and five other subunits that help keep Arp2 and Arp3 inactive. When required, the complex is...
Arp2/3 Complex
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01:26Introduction to Actin
Actin is a highly conserved cytoskeletal protein found abundantly in eukaryotic cells. It constitutes 10% weight of the total cellular protein in muscle cells, while in non-muscle cells, it is lower and makes up around 1–5 percent of the total cell protein. Actin found in the unicellular amoebae and complex multicellular animals is around 80% similar, demonstrating their conservation over a billion years of evolution. Actin coding genes are conserved within species and across different species.
01:19Actin Filament Depolymerization
Actin filaments (F-actin) are composed of actin subunits. The dissociation of actin monomers can occur from either end of F-actin. The rate of dissociation is faster from the minus-end or the pointed end, where the actin subunits exist with a bound ADP, together known as ADP-actin. The depolymerization of F-actin is aided by proteins, including the actin-depolymerizing factor (ADF) and cofilin family of proteins, gelsolin, and glia maturation factor (GMF).
In F-actin, the ADF/cofilin proteins...
In F-actin, the ADF/cofilin proteins...
02:54Nucleosome Remodeling
Nucleosomes are the basic units of chromatin compaction. Each nucleosome consists of the DNA bound tightly around a histone core, which makes the DNA inaccessible to DNA binding proteins such as DNA polymerase and RNA polymerase. Hence, the fundamental problem is to ensure access to DNA when appropriate, despite the compact and protective chromatin structure.
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Actin polymerization occurs through the head-to-tail association of binding sites on monomeric actin or G-actin to form filamentous or F-actin. The polymerization can be divided into three phases ̶ nucleation, elongation, and steady-state phase.
The nucleation phase involves forming a stable nucleus consisting of three actin monomers to form a new actin filament. Actin-binding proteins such as formins and Arp2/3 complex help filament growth post-nucleation. The Formins form straight actin...
The nucleation phase involves forming a stable nucleus consisting of three actin monomers to form a new actin filament. Actin-binding proteins such as formins and Arp2/3 complex help filament growth post-nucleation. The Formins form straight actin...
01:11Formation of Higher-order Actin Filaments
The polymerization of G-actin monomers into filamentous F-actin is a multi-step process. Once the F-actins are formed, they can bundle together in different arrangements to form higher-order networks and regulate cellular functions. Common examples include the formation of lamellipodia and filopodia at the cell's leading edge by actin reorganization in a migrating cell. The microvilli on the brush border epithelial cells are also formed through the F-actin network.
The high-order actin networks...
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