Plasmid storage conditions - (Jun/23/2014 )

Is it still safe to use a plasmid kept in water in the 4C fridge for 1 year?

Safe for what? - you shouldn't catch any illnesses from it so long as it isn't visibly growing something,

The only way to tell if it is useable is to run some on a gel and look at its integrity.

Depending on application, you might be better off transforming and doing a fresh prep.

yes, check it's integrity on a gel. it may have been acid hydrolyzed by the water (after absorbing co2 from the air).

If it was stored in TE rather than water, I'd say it is likely fine. If in water, then I would have doubts. Almost certainly you could transform it, which is what I would do immediately, then do a new prep.

How about -20 degrees Celsius for less than a year? Or would it be better to re-transform (i'm guessing take the old plasmid and transform it into new competent cells - please correct me if I'm wrong) and miniprep instead?

wswr on Fri Jan 15 01:39:51 2016 said:

How about -20 degrees Celsius for less than a year? Or would it be better to re-transform (i'm guessing take the old plasmid and transform it into new competent cells - please correct me if I'm wrong) and miniprep instead?

Plasmid should be in perfect condition when kept at -20C for a year.

Can't hurt to re-transform and miniprep fresh plasmid if you have any reason to be concerned about it (e.g. labmates dipping into it with dirty pipette tips, etc).