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Est DNA conc from phenolicky tissue?

Hiranya Roychowdhury hroychow at NMSU.EDU
Mon Oct 14 11:00:07 EST 1996

At 05:41 PM 10/14/96 +1000, Mike wrote:
>Does anyone know whether traces of phenolics in DNA can lead to an
>overestimate of DNA conc. using absorbance at 260nm?  Most of my
>extractions have a 260/280 of 1.8-2.0, but occasionally a 3-3.6 appears
>that leads me to suspect phenolics bound to the DNA may be producing
>screwy results.  I would expect my DNA to be too fragmented to allow for
>easy determination of concentration on an EtBr gel (the extent of
>shearing isn't really important for what I want the DNA for). 
>Any advice or ideas would be greatly appreciated.

Phenolics actually depress the ratio since they absorb more at 280nm. Clean
DNA shouldhave a ratio of 1.8. Higer ratio reflects hyperchromicity due to
very small fragmnts and/or free nucleotides.

Dr. Hiranya Sankar Roychowdhury
Plant Genetic Engineering Lab.
New Mexico State University
Las Cruces, NM 88003
Ph. (505) 646-5785
hroychow at nmsu.edu

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