Sequence heterogeneity in closed simian virus 40 deoxyribonucleic acid

Area of Science:

• Molecular Biology
• Virology
• Genetics

Background:

• Simian virus 40 (SV40) deoxyribonucleic acid (DNA) is a model system for studying viral DNA replication and genome stability.
• Understanding sequence homogeneity is crucial for interpreting experimental results and assessing viral integrity.

Purpose of the Study:

• To evaluate the sequence homogeneity of SV40 DNA under different propagation conditions.
• To characterize the types and frequencies of sequence alterations, specifically deletions and substitutions.

Main Methods:

• Formamide-protein film electron microscopy was employed to visualize and analyze heteroduplex DNA molecules.
• Self-annealing of denatured, singly nicked SV40 DNA allowed for the detection of sequence variations.
• Length measurements of heteroduplexes were used to distinguish between deletions and substitutions.

Main Results:

• SV40 DNA propagated at low multiplicity of infection (MOI) showed high sequence homogeneity with minimal deletions (approx. 2%).
• SV40 DNA passaged at high MOI or with undiluted lysates exhibited significant sequence alterations, with 7-13% deletions and 7-12% substitutions.
• Substitutions were confirmed as distinct from deletions and often resulted in shorter molecules, potentially incorporating host DNA.

Conclusions:

• High MOI or undiluted passaging of SV40 leads to substantial genomic instability, introducing both deletions and substitutions.
• Sequence variations, particularly substitutions, may involve the integration and excision of host cell nuclear DNA.
• Electron microscopy of heteroduplexes is a sensitive method for detecting and characterizing sequence heterogeneity in viral DNA.