Storing plasmid at 4 degrees C - (Mar/11/2009 )

I have plasmid prepared from maxi prep, and i am aliquoting them into 25ul portions and keeping them at -20C. I am using them for transfection, so i am planning to take each portion out for us and then keep it at 4 degrees C for a few days as I do the transfection. How long can the plasmid be kept at 4degrees C before it starts to breakdown?

Hi I never store my pDNA at -20C but keep it for at least one month at 4 degrees C without affecting my transfection efficiency (reagent I use = saint) in CHO-K1 cells. Normally I check it once / twice a month on agarose gel and concentration 260/280!
Good luck!

DNA is pretty stable at 4 degrees - I have kept DNA in the fridge for well over a year and it was still fine. So long s your tube doesn't get infected with bacteria or fungus, it should keep almost indefinitely. The reason it degrades when taken in and out of the freezer is due to the freeze/thaw cycles generating crystals that mechanically shear the DNA.

bob1 on Mar 11 2009, 03:10 PM said:

If the plasmid is in a buffer, like TE, it should last for weeks at 4C. However, if it's in MilliQ, the effective useable life drops quickly, especially after it's been opened (potential contamination).

I’ve ceped plasmids in the frige for 6 years without any problems. They were all in buffer (TE).

Swanny said correctly that in MilliQ, the effective useable life drops quickly. This is because the DDW with 18.2 ohm is acidic (~pH=5)