Formamide extraction of lambda?

Amy Teel amy at molbio.cbs.umn.edu
Mon Aug 16 07:25:14 EST 1993

Helgi Briem Magnusson (hbriem at rhi.hi.is) wrote:
: After running a lambda lysate on a CsCl gradient I was about 
: to extract the DNA using our usual method, dialysis,
: 3x phenol and chloroform extractions and dialysis again, 
: when I came across an alternate protocol in Ausubel's Red Book
: section 1.13.3.  This involves adding very strong Tris/EDTA and
: formamide, letting it sit for half an hour, then adding EtOH,
: quick spin and wash with 70% EtOH.  This method seems so easy
: that I figure there must be a catch to it.  Has anyone out
: there tried this formamide protocol and are they happy with it?
: Are there any problems with it?  How about yield?

I have used this method before and it works GREAT. The idea (or so I have
been told) is that the formamide causes the lambda particles to "eject"
their DNA in some mysterious manner.  Anyway, it's always worked well for
me, as long as the the lambda yield from the CsCl gradient was decent (in
other words, if I could see even a faint blue band, I got lots of DNA).
I never had any problems cutting the DNA, either.

Try it!

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