Hiranya S. Roychowdhury hroychow at
Tue May 16 10:01:57 EST 2000

At 10:50 AM 5/16/00 +0100, Richard P. Grant wrote:

>> When using isopropanol for DNA precipitation, is it necessary to add any
>> kind of salt before? 
>No, there is no need to add salt.  Be careful not to leave the ppt too 
>long at low temp as you can get a lot of protein coming down.  What is 
>the particular application here?

Are you sure about this, Richard? I have never been able to get pptn w/o
salt unless I had a very high conc. of DNA.

Indeed, I sometimes store my DNA/RNA in  2-propanol till I'm ready to use
it. And then I add KOAc to ~0.3M to ppt the it out.

>> I have read that after isopropanol precipitation it
>> is a good idea to wash the pellet to remove coprecipitated staff. This
>> washing should be with 70% isopropanol, ethanol or what ?
>70% Ethanol is a good idea, but if you want to be rigorous you should 
>resuspend the pellet and reprecipitate with acetate/ethanol.

The 70% etoh wash is to get rid of salt following the "salt-alcohol" pptn of
DNA (or RNA). So, repptn of the NA w/ "acetate/ethanol" will definitely
yield cleaner stuff, but the 70% etoh (or 50% 2-propanol) wash cannot be
dispensed with if salt in DNA is not welcome.

>Richard P. Grant MAD Phil    
>Please reply to rpg 'at''
>         Sex and bugs and rock and roll

Dr. Hiranya Sankar Roychowdhury
New Mexico State University
Las Cruces, NM 88003
Ph. (505) 646-5785
hroychow at


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