Blot Blocking Agent

Mark Schweder mschweder at
Sun Jul 18 20:23:00 EST 1993

Folks in this lab for years used Salmon Sperm DNA (SIGMA PN# D1626) as a 
blocking agent for Southern and Northern blots. The stuff costs about $200 
for 10g. In addition it was quite diffucult to prepare. It had to be soni- 
cated or vortexed or run through a hypodermic needle to break it into 
adequately sized pieces. The process sometimes took hours and was usually 
relegated to the dishwasher person.

One day while looking through the SIGMA catalog, I ran across something 
called DNA Degraded Free Acid From Herring Sperm (PN# D3159) which costs 
about $10 for 10g. It sounded like what we had been spending lots of money 
and time preparing. I ordered some and it easily dissolved in a basic 
solution and works wonderfully as a blocking agent for Southern and Northern 
blots. It costs 1/20 the Salmon Sperm DNA and is easily prepared. If you 
have $10 to burn give it a try.

   Mark Schweder                | There are three things that smell like fish!
   Plant Science Laboratory     | One of them is fish...
   Agronomy Department          | The other two...
   University of Florida        | Are growing on you...
   Gainesville, Florida 32611   | (Frank Zappa, Jumbo Go Away)
           904-392-1890         |         mschweder at
                  DISCLAIMER: I know nothing about nothing.

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