Mechanism of chromatin remodeling factor

Posted by MeganBowie on February 1st, 2021

There are many kinds of chromatin remodeling factors in eukaryotic cells, most of them exist in the form of protein polymers. Different chromatin remodeling factors are located on specific native nucleosomes and recombinant nucleosomes at specific time, which affect gene transcription activity by changing chromatin structure, thus ensuring the correct operation of various biological processes in cells.

Highly folded chromatin structure is necessary for its packaging into the nucleus, but this dense chromatin hinders gene transcription, DNA replication and damage repair of corresponding chromatin sites. Therefore, with the evolution of eukaryotes, a group of chromatin remodeling enzymes and some related protein factors have been produced, which regulate the structure of chromatin by regulating the assembly, disassembly and rearrangement of nucleosomes on chromatin. Among them, one kind of proteins can use the energy produced by ATP hydrolysis to drive nucleosomes to "slide" on DNA, or mediate the "replacement" between histone variants and classic histones in nucleosomes. These proteins are ATP dependent chromatin remodeling factors, which usually consist of multiple subunits to form a chromatin remodeling complex with larger molecular weight.

In eukaryotic cells, chromatin remodeling factors regulate chromatin structure by changing the assembly, disassembly and rearrangement of nucleosomes on chromatin, so as to improve the local accessibility of transcription related factors such as transcription factors in chromatin DNA. When the chromatin structure tends to become loose under the action of chromatin remodeling factors, the accessibility of RNA polymerase II and transcription factors to chromatin DNA is increased, thereby initiating gene transcription. On the contrary, when the chromatin structure tends to be dense, the accessibility of RNA polymerase II and transcription factors to the chromatin DNA is weakened, thereby inhibiting the transcription of related gene.

Mediated nucleosome "sliding"

It is well known that DNA helicase is a kind of protease that opens the double helix of DNA depending on the energy released by ATP hydrolysis. It is divided into six subfamilies. Among them, the SF2 family helicase can usually bind double stranded DNA and move along the single strand in a specific direction, leading to the separation of double strands. Although the ATPase subunit of SNF2 chromatin remodeling complex family does not have the activity of SF2 like helicase, it still has a similar mechanism of action. It has been proved that the chromatin remodeling complex family has the function of DNA translocase, that is, it can make the nucleosome slide along the DNA when the DNA double strand is not broken.

Mediated nucleosome replacement

Most of the nucleosomes in chromatin are composed of four kinds of classical histones, but some of them can be replaced by histone variants. The nucleosomes containing histone variants are specially labeled on chromatin, and the specific structural characteristics of different variants make the chromatin structure change to some extent, which mediates the changes of corresponding cell function. It has been found that some chromatin remodeling complexes are the executors of histone variant substitution into (or out of) nucleosomes. The most typical example is that in yeast, swr1 can catalyze the substitution between h2az-h2b heterodimer and classic H2A-H2B dimer in nucleosomes.

Conclusion and Prospect

In recent years, epigenetic regulation as an important role in maintaining the stability of intracellular environment has attracted more and more attention, and chromatin remodeling factor is one of the important components. At present, there are more and more methods to study chromatin remodeling complex, and the means are more and more advanced. We firmly believe that with the continuous improvement of electron microscopy and biological experimental technology, we are looking forward to unveiling the mystery of chromatin remodeling complex in the near future.

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