SV40 minichromosome composition — histone association Which histone is notably absent from the SV40 virion-associated minichromosome?

Introduction / Context:
SV40 packages its circular DNA with host histones, forming a minichromosome that resembles nucleosome organization in eukaryotic chromatin. However, the histone composition is distinctive compared with bulk chromatin.

Given Data / Assumptions:

• Standard core histones: H2A, H2B, H3, H4.
• Linker histone: H1 stabilizes higher-order chromatin in many eukaryotes.
• SV40 virions contain nucleosome-like particles.

Concept / Approach:
Analyses of SV40 chromatin show association with core histones H2A, H2B, H3, and H4 that form nucleosomes. The linker histone H1 is not a stable component of the packaged viral minichromosome inside virions. This difference is often tested to distinguish core nucleosome assembly from higher-order chromatin organization.

Step-by-Step Solution:

Verification / Alternative check:
Biochemical isolation of SV40 chromatin demonstrates core histones present, with H1 largely absent from mature virions.

Why Other Options Are Wrong:

• H2A, H2B, H3, H4 are core histones detected in SV40 chromatin.

Common Pitfalls:
Assuming viral chromatin mirrors all aspects of host chromatin; virions streamline components for packaging.

Final Answer:
H1