nicking DNA plasmids on purpose

Ned Mantei mantei at
Sat Mar 2 09:45:06 EST 1996

In article <31374522.58D1 at>, walberg at wrote:

> Sorry I missed the beginning of this, but if you want to isolate open 
> circles (form II) then there are some published methods to do this.  
> An interesting one was published in NAR in 1975 or 1976 or so 
> by Phil Martens and David Clayton.  They nicked circular DNA in the 
> presence of ethidium using a strong visible light- a slide projector I 
> think.  I think they got it to work with very good efficiency with 
> very little form III.

The procedure was more or less to have DNA plus fairly concentrated EtBr
(perhaps 10--50 ug/ml?) in a cuvette. Illuminate with a slide projector
about 10 cm away, meanwhile cooling with a fan or hairdrier. Times to get
nicked circles were in the range of minutes. The method was around at
least a year or two before 1975.

Ned Mantei
Dept. of Neurobiology, Swiss Federal Institute of Technology
CH-8093 Zurich, Switzerland
mantei at   Fax: +41-1-633-1046

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