![]() ![]() ![]() Specific protein complexes, known as histone-modifying complexes catalyze addition or removal of various chemical elements on histones. ATP-dependent chromatin remodeling complexes.Ĭovalent histone-modifying complexes.To overcome this issue and allow dynamic access to condensed DNA, a process known as chromatin remodeling alters nucleosome architecture to expose or hide regions of DNA for transcriptional regulation.īy definition, chromatin remodeling is the enzyme-assisted process to facilitate access of nucleosomal DNA by remodeling the structure, composition and positioning of nucleosomes.Īccess to nucleosomal DNA is governed by two major classes of protein complexes: Such condensed structure occludes many DNA regulatory regions, not allowing them to interact with transcriptional machinery proteins and regulate gene expression. However, DNA is tightly packaged in the nucleus with the help of packaging proteins, chiefly histone proteins to form repeating units of nucleosomes which further bundle together to form condensed chromatin structure. The transcriptional regulation of the genome is controlled primarily at the preinitiation stage by binding of the core transcriptional machinery proteins (namely, RNA polymerase, transcription factors, and activators and repressors) to the core promoter sequence on the coding region of the DNA. Nucleosome positioning and chromatin compaction can be influenced by a wide range of processes including modification to both histones and DNA and ATP-dependent chromatin remodeling complexes. Euchromatin (loose or open chromatin) structure is permissible for transcription whereas heterochromatin (tight or closed chromatin) is more compact and refractory to factors that need to gain access to the DNA template. The level of nucleosomal packaging can have profound consequences on all DNA-mediated processes including gene regulation. Targeting chromatin remodeling pathways is currently evolving as a major therapeutic strategy in the treatment of several cancers.Ĭhromatin organization: The basic unit of chromatin organization is the nucleosome, which comprises 147 bp of DNA wrapped around a core of histone proteins. Aberrations in chromatin remodeling proteins are found to be associated with human diseases, including cancer. Besides actively regulating gene expression, dynamic remodeling of chromatin imparts an epigenetic regulatory role in several key biological processes, egg cells DNA replication and repair apoptosis chromosome segregation as well as development and pluripotency. ![]() Such remodeling is principally carried out by 1) covalent histone modifications by specific enzymes, e.g., histone acetyltransferases (HATs), deacetylases, methyltransferases, and kinases, and 2) ATP-dependent chromatin remodeling complexes which either move, eject or restructure nucleosomes. Chromatin remodeling is the dynamic modification of chromatin architecture to allow access of condensed genomic DNA to the regulatory transcription machinery proteins, and thereby control gene expression. ![]()
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