Question

Which ONE of the following histone protein(s) is known as "linker histone"?

• A. H1
• B. H2A and H2B
• C. H3
• D. H4

Hint:

Histones: Core Histones = H2A, H2B, H3, H4 (Octamer). Linker Histone = H1 (Stabilizes 30nm fiber).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Chromatin nucleosome core architecture consists of an octamer of core histones, with a distinct linker histone securing the entry and exit DNA strands.
Key Formula or Approach:
\[ \text{Nucleosome Core Octamer: } 2 \times (\text{H2A, H2B, H3, H4}) + \text{Linker Histone: } \text{H1} \]

Step 2: Detailed Explanation:
Chromatin structural proteins:
1. Core Histones: Two copies each of H2A, H2B, H3, and H4 assemble into an octameric cylindrical core around which 146--147 bp of DNA wraps in $1.67$ left-handed superhelical turns.
2. Linker Histone (H1): Binds to the entry/exit DNA at the base of the nucleosome core particle and associates with the $\approx 20 - 80\text{ bp}$ linker DNA, sealing the nucleosome and facilitating the folding of the 10-nm 'beads-on-a-string' fiber into the higher-order 30-nm chromatin solenoid.

Step 3: Final Answer:
Thus, Histone H1 is known as the Linker histone, matching option (A).