Plasmid DNA quality for transfection - Is CsCl prep ever required? (Nov/16/2006 )

I'm having problems with low transfection efficiency and I think I've ruled out everything except DNA quality. I prepared my DNA by Qiagen MIDI prep and my boss suggested I do a CsCl prep as well.

Did anyone find that you have to use a CsCl prep to get good transfection efficiency with certain plasmids?

Also, any advice on how to get the best quality DNA using a Qiagen MINI prep kit?

I appreciate any help and advice.

What's the A260/A280 ratio? Have you run your DNA on a gel to see if it's still intact?

What cells are u transfecting with which reagent? Mostly, bad transfection efficiencies are due to the reagent used not being suitable for your cells, or just your cells being difficult to transfect.

Something you might take into account is endotoxins being present in your DNA, but that would result in same transfection efficiency but more toxic effects.

I'm agree with vairus, I'd suspect on other conditions before QIAGEN kit.

Thanks for your replies, vairus and aleruiz. I think I will post a new question outlining the whole low transfection efficieny problem.