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CK Wen cwen at aux.btny.purdue.edu
Sun Nov 5 10:26:46 EST 1995

The department I am joining has tissue samples that have been frozen
away for years and they want me to do RT-PCR on the samples. The
samples were not taken originally for molecular biology and so have
been placed in non sterile clean tubes (not autoclaved though) and were
flash frozen in liq N2 and stored at -20 and -80. Does anyone out there
know how long samples can be kept frozen before analysis. Will the RNA
have degraded?
I was planning on adding the guanadinium as the samples were thawing
and homogenize them on thawing.

Any advice or papers you know that may help would be much appreciated


Heather Medbury
    I do not know if you can isolate good RNA or not. However, I may 
give you my suggestions.  
1. Try to isolate RNA from fresh tissue and the frozen tissue which you 
are working with at the same time.  If you can get good RNA from the 
fresh tissue but not from the old frozen tissue, in several repeats, 
then it might indicate that the old frozen tissue is bad.
2.  I have several poly(A)RNA which have been stored at -70C for more 
than 2 years and they look good when I do a Northern hybrodization.
3. In one of my experience, I isolated rice callus which was stored at 
-20C and the RNA I got was bad. However, it was only done only ONCE, and 
I did not know if it was the problem of storage or my operation. For 
some tissues which have been stored at -70C for more than one year, the 
RNA I isolated was very good.\

Hope it helps.  Good luck.


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