southern size standards

peter via (by peter.ianakiev from
Thu Jun 26 07:03:02 EST 2008

On Jun 25, 3:38 pm, Ed Siefker <ebs15... from> wrote:
> 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?

Just stain the membrane with ethidium Br  or other fluorescent dye.
After the transfer you usually can see your ladder quite well. In
Southern (depending on the complexity) it is difficult to avoid seeing
the ladder due to non-specific hybridization .

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