Histone octamer

Basic units of chromatin structure

File:Histone Octamer x-ray structure.jpg

Histone Octamer x-ray structure

Nucleosome structure

== Histone Octamer ==

The histone octamer is a protein complex that plays a crucial role in the packaging of DNA into chromatin in eukaryotic cells. It is composed of eight histone proteins: two each of histone H2A, histone H2B, histone H3, and histone H4. These histones form a core around which DNA winds, facilitating the compaction of DNA into the highly organized structure of chromatin.

Structure

The histone octamer is an octameric assembly of histone proteins. Each histone protein has a characteristic structure that includes a central histone fold domain, which is involved in the formation of the histone octamer. The histone fold domain consists of three alpha helices connected by two loops. The histone octamer is formed by the interaction of these histone fold domains, creating a stable core around which DNA can wrap.

Function

The primary function of the histone octamer is to package DNA into nucleosomes, the fundamental units of chromatin. Each nucleosome consists of approximately 147 base pairs of DNA wrapped around a histone octamer. This packaging reduces the length of DNA by about one-third, making it more compact and manageable within the cell nucleus. The histone octamer also plays a role in regulating gene expression by controlling the accessibility of DNA to transcription factors and other regulatory proteins.

Assembly

The assembly of the histone octamer is a highly regulated process that occurs in the cell nucleus. Histone proteins are synthesized in the cytoplasm and then transported into the nucleus, where they undergo post-translational modifications. These modifications, such as acetylation, methylation, and phosphorylation, can influence the assembly and stability of the histone octamer. The histone proteins then interact with each other to form the histone octamer, which subsequently associates with DNA to form nucleosomes.

Histone Variants

In addition to the canonical histones, there are several histone variants that can replace the standard histones in the octamer. These variants, such as H2A.Z, H3.3, and CENP-A, can alter the properties of the nucleosome and influence chromatin structure and function. Histone variants are often involved in specific cellular processes, such as DNA repair, transcriptional regulation, and chromosome segregation.

Related Pages

• Chromatin
• Nucleosome
• Histone
• DNA
• Gene expression
• Post-translational modification
• Transcription factor