southern size standards

[Jose de las Heras]

"Ed Siefker" <ebs15242 from creighton.edu> wrote in message 
news:mailman.560.1214432240.3533.methods from net.bio.net...
> 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?


I tend to simply add a *minute* amount of the ladder to my probe during the 
labelling reaction. Then you see the ladder as well as your probe... but of 
course, you have to be sure there won't be crosshybridisation.

Jose