2. Incubate the cells at 37C in a CO2 incubator until the cells are 70-80% confluent. This will usually take 18-24 h.
3. Prepare the following solutions in 12 x 75 mm sterile tubes:
Solution A: For each transfection, dilute 2 µg DNA (plasmid) in 375 µl serum-free basal medium
Solution B: For each transfection, dilute 12 µl LIPOFECTAMINE Reagent in 375 µl serum-free medium
4. Combine the two solutions, mix gently, and incubate at room temperature for 15-45 min. The solution may appear cloudy, however this will not impede the transfection.
5. Wash the cells once with 2 ml serum-free medium.
6. For each transfection, add 750 µl serum-free medium to each tube containing the lipid-DNA complexes. Do not add antibacterial agents to media during transfection. Mix gently and overlay the diluted complex solution onto the washed cells.
7. Incubate the cells for 5 h at 37C in a CO2 incubator.
8. Add 1.5 ml medium with 20% FBS without removing the transfection mixture. If toxicity is a problem, remove the transfection mixture and replace with normal growth medium.
9. Replace medium at 18-24 h following start of transfection.
10. Assay cell extracts for gene activity 24-72 h after the start of transfection, depending on cell type and promoter activity or add selective antibiotic for isolating stable transformants.