octamer

An octamer is an assembly or object composed of eight subunits, monomers, or components. The term is used across disciplines such as biochemistry, molecular biology, and materials science to describe eight-part structures. In biology, many octameric assemblies are protein complexes; a well-known example is the histone octamer, the core around which DNA is wrapped in the nucleosome.

The histone octamer consists of two copies each of histones H2A, H2B, H3, and H4. About 147 base pairs of DNA are wrapped around this octamer to form the nucleosome core particle, which is the fundamental unit of chromatin in eukaryotic cells. Histone octamers can be disassembled and reassembled during processes such as transcription, replication, and DNA repair, with the help of histone chaperones and chromatin-remodeling factors. Octameric protein assemblies can also occur in other contexts, including various ring- or barrel-shaped complexes with eight subunits.

In gene regulation, octamer-binding transcription factors recognize regulatory DNA sequences known as octamer motifs and help control transcription of target genes. Members of the octamer-binding factor family include various POU-domain proteins, such as Oct-1 and Oct-4, which bind to these motifs to influence developmental and cellular programs.

Beyond biology, the term octamer can describe eight-unit oligomers or clusters in chemistry and materials science, where eight monomeric units assemble into larger structures. The specific composition and geometry of octamers vary by system and application.