EtBr ussage

Stephen Gisselbrecht gisselbr at
Fri Jun 18 14:18:29 EST 1993

In article <1993Jun18.152949.1 at> brennanp at writes:
>I once heard an interesting suggestion that instead of soaking
>the gel in EtBr to add small amount of EtBr soln to the samples
>before running the gel.  It still allows visualation but does
>not require the large amts of EtBr reqd for soaking gels.
>Paul Brennan, Trinity College, Dublin, Ireland

	This is essentially what I do when running RNA gels for Northerns,
and people in my current lab do it with DNA too--works just fine.  You
don't need much at all!  If you're currently casting your gels with EtBr
in them, as I usually do, this is approximately equivalent.  The only
possible reason not to do these is that ethidium bound to DNA will change
the way it runs--this is why some people are religious about the fact that
you must ONLY stain with EtBr by soaking the gel after running it.  As
long as you're running linear fragments, you can ignore this; ethidium
binds to all the sample DNA and all the standards and so everything runs
the same relative to everything else on the gel.  If you're interested in
supercoiled and nicked circular species, however, then I think this
becomes important, as the degree of supercoiling affects the amount of
EtBr that can bind to a given amount of DNA. (This, unless I've been
misled, is the principle behind CsCl gradient purification of plasmid

					steve gisselbrecht
					cell & dev. bio.
					harvard medical school

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