Brett Lindenbach Brett_Lindenbach at QMS1.LIFE.UIUC.EDU
Mon Jun 22 14:09:09 EST 1992

        Reply to:   RE>None

>Cosmid preps (minipreps of cosmid harbouring Ecoli) yield
>good amounts of vector DNA when tested undigested. However when
>tested by restriction with EcoRI, smeared as if nicked or sheared.
This >was not due to the restriction enzyme since incubation with
>alone yielded the same picture. Then my tech suspected the RNASE A
>which she used during the prep and indeed a second miniprep without
>RNASE treatment proved OK both with and without EcoRI digestion (or
other enzymes).
Fred Van Leuven
Center for Human Genetics - Leuven - Flanders (part of Belgium)
Acknowledge-To: <FRED at BLEKUL13>

Sounds to me like DNAse in your RNAse. Unless you specifically bought
DNAse-free RNAse, it needs to be treated. The simplest solution would
be to make up a fresh batch, and heat to 90C for 15 min., as per
Sambrook & Maniatis.
 Brett Lindenbach
Univ. Illinois Dept. Microbiology
brett_lindenbach at

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