Linker DNA and histone association in nucleosomes Within chromatin architecture, which histone is primarily associated with linker DNA and helps stabilize higher order structure?

Difficulty: Easy

Correct Answer: Histone H1

Explanation:


Introduction:
Nucleosomes compact eukaryotic DNA by wrapping it around histone octamers. Beyond the core histones, an additional histone associates with linker DNA between nucleosomes and contributes to chromatin fiber organization and stability.


Given Data / Assumptions:

  • Core nucleosome contains two copies each of H2A, H2B, H3, and H4 with about 146 base pairs of wrapped DNA.
  • Linker DNA connects adjacent nucleosomes and varies in length by cell type and species.
  • A distinct histone binds at the dyad and engages linker DNA, promoting compaction.


Concept / Approach:

Histone H1, often called the linker histone, binds near the nucleosomal dyad and contacts linker DNA. This reduces DNA accessibility and promotes formation of higher order fibers, modulating gene regulation by changing chromatin openness.


Step-by-Step Solution:

1) Identify core versus linker associated histones.2) Recognize H1 function at the entry and exit points of DNA on the nucleosome.3) Conclude H1 is the principal linker associated histone.


Verification / Alternative check:

Biophysical studies show that H1 binding compacts arrays into higher order structures. Knockdown experiments increase chromatin accessibility, validating this role.


Why Other Options Are Wrong:

H2A, H2B, H3, and H4 form the core octamer, not the linker binder. CENP A is a centromeric H3 variant specific for kinetochore chromatin, not general linker association.


Common Pitfalls:

Assuming all histones behave identically or confusing H1 with core histones. Another pitfall is equating histone variants with linker function without evidence.


Final Answer:

Histone H1

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