SV40-based delivery: Recombinant SV40 viruses introduce foreign DNA into mammalian cells in what way?
Correct Answer: Without DNA-mediated transfection (via viral infection)
Introduction / Context:Simian Virus 40 (SV40) is a DNA tumor virus historically used as a cloning and expression vector in mammalian systems. Recombinant SV40 particles enter cells using viral entry mechanisms, bypassing classical chemical or physical transfection procedures.
Given Data / Assumptions:
- Recombinant SV40 vectors are packaged into infectious virions.
- Viruses naturally deliver their genomes to host cells.
- “DNA-mediated transfection” refers to methods like calcium phosphate, lipofection, or electroporation.
Concept / Approach:Infection by an SV40 virion introduces the recombinant DNA directly through receptor-mediated entry, uncoating, and nuclear import of the viral genome. Therefore, one does not require separate DNA transfection protocols to achieve delivery—viral infection accomplishes it.
Step-by-Step Solution:
Identify that the vector is delivered as an infectious particle.Recall that infection replaces the need for chemical/physical transfection methods.Choose the option that states delivery occurs without DNA-mediated transfection.Verification / Alternative check:Standard SV40 vector protocols rely on generating high-titer stocks and infecting cells, confirming that infection is the delivery route.
Why Other Options Are Wrong:
- With DNA-mediated transfection: unnecessary when using infectious virus.
- RNA-mediated transfection: irrelevant for a DNA virus system.
- Lipid fusion only or microinjection: not the typical SV40 delivery route.
Common Pitfalls:Confusing transfection (non-viral) with transduction (viral delivery).
Final Answer:Without DNA-mediated transfection (via viral infection)