Final answer:
A nucleosome contains five types of histone subunits: two copies of each core histones H2A, H2B, H3, and H4, as well as a single linker histone H1, essential for DNA compaction and gene regulation.
Step-by-step explanation:
There are five different types of histone subunits present in a nucleosome. These include two copies each of the four core histones: H2A, H2B, H3, and H4. Together, they form an octamer around which the DNA wraps. Additionally, there is a single linker histone, H1, that binds to the nucleosome, helping to stabilize the structure and facilitate further compaction of the chromatin fiber.
The core histone proteins are responsible for the initial level of DNA compaction, where approximately 146 base pairs of DNA wrap around the histone octamer to form the bead-like structure known as a nucleosome. This organization is essential for the efficient packaging of DNA within the nucleus and plays a significant role in the regulation of gene expression.