southern size standards

Kay Schink via (by k.schink_nospam_ from
Fri Jul 4 04:51:23 EST 2008

Ed Siefker schrieb:
> I'm looking for a DNA size standard I can use with southern blots.  I don't
> want to deal with radioactive gel apparatus, so I don't want to end label
> my ladder before I run the gel.  The ideal solution would be something dyed
> so I could see with the naked eye on the membrane, and mark the sizes with
> radioactive ink.  Is there something like this available?
> Here's an idea, I can see the DNA ladder in my gel under UV.  Could I 
> inject
> a small amount of P32 into each size standard, and then transfer so the 
> size
> standards would be visible on the membrane?
> I've seen protocols for making size standards from lambda DNA, but these
> require probing with lambda DNA.  If I do this, would I include the lambda
> probe in the hybridization with my probe?  Do I need to reprobe with the
> lambda probe?
In our lab, we have frequently observed cross-hybridisation of labelled 
probes with the DNA Ruler Ladder Mix from Fermentas (no affiliation). 
Interestingly, this happens only with this marker, but not with others 
like Lamba-Pst - so you could give it a try if this wouks with your 
probes, too. We also usually photograph our gels with a ruler next to 
it, so by measuring the distance from the wels to our band, we can 
interpolate the sizes.

Good luck


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