Southern blot mystery

[Joe Appelgryn]

I've done a slot blot, using a MINIFOLD II system with different
concentrations of genomic DNA and a purified fragment, the same as my probe,
as a control.  The detection is by means of chemiluminescent methods, using
DIG nonradioactive detection system from Roche Molecular Biochemicals (also
Boerhinger-Mannheim).  The first time I did the slotblot you could see the
bands perfectly.  When I repeated the blot with the same DNA, and other
conditions, the result was unexpected.  The purified fragment, used as
control, came out as a black band but the rest of the bands appear white on
the x-ray film.  I was told that it is negative staining, but nobody could
told me what the possible cause might be.  I also don't know if you could
see it as a "positive" result, or was there simply no DNA transfered.
I would appreciate it if somebody could help me.

Joe Appelgryn
Department of Botany and Genetics
University of the Free State
Bloemfontein
South Africa


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