Cloudy DNA

Aaron Engelhart aaron.engelhart at gmail.com
Mon Aug 23 04:23:43 EST 2004

We do some work with calf thymus DNA at high concentrations (3-7
millimolar) in milliliter quantities for spectrophotometry/transient
absorption spectroscopy purposes. One problem is that it seems to be
fairly cloudy above the millimolar level. This is the cheapest source
of DNA, so I like to use it for obvious reasons before doing
experiments on synthetic oligos or polyG-polyC, etc, but the
cloudiness is a problem. I have done some work with phenol extraction,
which seems to help a bit, but with significant product loss. Every
time I do a phenol extraction, there is a bit of whitish gunk at the
interface. I don't understand the mechanics of this completely, or
exactly what it is. There's some obvious product loss from leaving a
bit of the supernatant behind to avoid taking up the impurity, but my
understanding is that the dsDNA stays in the aqeuous phase and the
proteins go into the organic phase. A260/280 ratio looks fine (and
unchanged!) before and after extraction. Does anyone have a good way
to clear up CTDNA/know what this is? TIA,


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