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Nucleosome-like structural subunits of intranuclear parental adenovirus type 2 DNA
Abstract:
The intranuclear structure of parental adenovirus 2 DNA was studied using digestion with micrococcal nuclease as a probe. When cultures were infected with 32P-labeled virions, at a multiplicity of 3,000 particles per cell, 14 to 21% of parental DNA penetrated the cell and reached the nucleus. Of this parental DNA, 60% could be solubilized by extensive digestion with micrococcal nuclease. The nuclease-resistant fraction contained viral deoxyribonucleoprotein monomers and oligomers. These nucleosome-like structures contained DNA fragments which are integral multiples of a unit-length DNA of approximately 185 base pairs. The monomeric DNA is similar in length to the unit-length DNA contained in cellular nucleosomes. However, the viral oligomers are slightly smaller than their cellular counterparts. DNA-DNA hybridization demonstrated that all segments of the viral genome, including those expressed as mRNA only at late times, are represented in the nucleosomal viral DNA. The amount of early intranuclear viral chromatin was proportional to multiplicity of infection up to multiplicities of 4,000 particles per cell. However, viral transcriptional activity did not increase in direct proportion to the amount of viral chromatin. Maximum accumulation of intranuclear viral chromatin was achieved by 3 h after infection. The intranuclear parental viral chromatin remained resistant to nuclease digestion even at late times in infection, after viral DNA replication had begun.
Insights
Parental adenovirus 2 DNA forms nucleosome-like structures within the host cell nucleus. These structures, resistant to micrococcal nuclease, contain DNA fragments of approximately 185 base pairs, suggesting a unique viral chromatin organization.
Area of Science:
- Molecular Biology
- Virology
- Chromatin Structure
Background:
- Adenovirus DNA enters the host cell nucleus after infection.
- The intranuclear organization of viral DNA is crucial for understanding viral replication and gene expression.
Purpose of the Study:
- To investigate the intranuclear structure of parental adenovirus 2 DNA.
- To determine the nuclease accessibility and organization of viral DNA within the host cell nucleus.
Main Methods:
- Infection of cell cultures with 32P-labeled adenovirus 2 virions.
- Micrococcal nuclease digestion to probe DNA accessibility.
- DNA-DNA hybridization to assess genome representation in nucleosomal DNA.
Main Results:
- 14-21% of parental adenovirus DNA reached the nucleus, with 60% being micrococcal nuclease-sensitive.
- A nuclease-resistant fraction contained viral deoxyribonucleoprotein monomers and oligomers with nucleosome-like structures.
- These structures contained DNA fragments of approximately 185 base pairs, with viral oligomers being smaller than cellular counterparts.
- All viral genome segments were represented in the nucleosomal viral DNA.
- Intranuclear viral chromatin accumulated by 3 hours post-infection and remained nuclease-resistant even at late infection times.
Conclusions:
- Parental adenovirus 2 DNA is organized into nucleosome-like structures within the host cell nucleus.
- These viral chromatin structures are resistant to nuclease digestion, indicating a stable organization.
- The organization of viral DNA into nucleosomes may play a role in regulating viral gene expression and replication.