Freezing PCR products

[Paul N Hengen]

 In article <1994Mar11.135900.29812 at alw.nih.gov>
 Jim Owens <jow at helix.nih.gov> writes:
 
> In article <9403102355.AA08771 at unixsrv1.lsumc.edu> Marion Freistadt,
> mfreis at lsumc.edu writes:
 
>> A colleague of mine says that freezing a PCR product makes it disappear.
>> Does anyone have any information on this subject?  The topic came up when a
>> PCR product was frozen prior to gel analysis.  My colleague attributed the
>> absence of product to freezing.  Naturally we are testing it.  The
>> identical reaction did work a few days ago.
 
I really think you hit a bad PCR reaction and that freezing had nothing
to do with a lack of product. You should of course take out a sample
from the _same_ tube before freezing as a control if you are to test this.

> I have not frozen PCR products.  Instead I store them at 4oC in TE.  I
> would assume that a single freezing should not hurt them.  I would expect
> them to behave like restriction fragments.
 
I always store DNA at -20oC in H2O. I've never had a problem.

> Now for my standard ramblings on freezing:
>
> When I was a grad student my advisor was an organic chemist who found
> greater academic opportunities in biochemistry and had fled to a biology
> department in a large university.
>
> At a journal club he presented a paper by a physical chemist who had
> studied freezing drops of aqueous solutions by different methods: placing
> in a deep freezer; placing on dry ice; placing in acetone/dry ice bath;
> placing on liquid nitrogen.  There was a pH gradient in the samples
> frozen by all means except liquid nitrogen.  The gradient went from
> highest pH at the periphery to lowest pH in the center, the last part
> frozen.  And the gradient was higher (greater) in the slower freezing
> methods than in the faster ones.
...[rest deleted]...

Interesting enzyme story. Did he ever try to store the enzymes using these
different methods, or just feel confident about what he was doing? :-)
 
About the PCR fragment...I have a reference to DNA being put through freeze-
thaw cycles with no apparent damage. I'd expect a single freeze at -20oC
would not cause your DNA to disappear.

@article{Anonymous1983,
author = "Anonymous",
title = "Does freezing and thawing of {DNA} solutions
insert nicks in the double helix?",
journal = "B.R.L. Focus",
volume = "5",
number = "2",
pages = "10",
year = "1983"}
 
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