Les Hoffman lhoffman at midplains.com
Wed Aug 28 14:29:42 EST 1996

        RE: UV Safe TAE 
        Wed, 28 Aug 1996 12:26:23 -0700 
        Les Hoffman <lhoffman at midplains.com>

There seems to be some misinformation here concerning the nature of the
damage done to DNA by UV transilluminators.  Yes-- long- (305-315 nm) or
shortwave (260 nm) UV transilluminators can cause the formation of
cyclobutane pyrimidine dimers (CPD's) in adjacent pyrimidine residues of
DNA. But no-- there is not normally "breakage" of the DNA by UV light
alone. Certain endonucleases (such as T4 endo V) may cleave the
phosphodiester bonds adjacent to the site of CPD's, or the CPD's may
block replication of the segment of DNA with UV damage.
At any rate, it's good practice to avoid UV exposure of DNA which is to
be cloned.  We run an adjacent pair of marker lanes containing the same
DNA sample, cut out the "prep" lane to be cloned without UV exposure, and
mark the positon of the desired band(s) in the marker lanes with a blunt
pencil tip during UV transillumination.  After repositioning the prep
lane next to the marker lanes, you can cut out the desired bands and
purify the DNA without UV damage.
Les Hoffman
Epicentre Technologies

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