Northern background

[Klaus.Matthaei at ANU.EDU.AU]

With regard to Southerns we (and the FBI) have found that stripping in 55%
formamide, 2xSSPE, 1% SDS at 65*C for 60-90 minutes results in the cleanest
removal of probe and the least loss of target (i.e. can reprobe MANY times
e.g. 8-10 times).  

With regard to background from large probes we always acid depurinate the
probe to shear to about 500bp since this gives the best signal.  

When we see a huge  background on the top half of our blot i.e. high MW end
it is I believe due to a dirty electrophoresis tank that has been used to
run plasmids etc. i.e. DNA contamination in the buffer that then
electrophoreses into the gel.

Good Luck, Klaus
--------------------------------------------------------------------------
Klaus Matthaei
Gene Targeting
The John Curtin School of Medical Research
The Australian National University
E-mail: Klaus.Matthaei at anu.edu.au

"Think twice - Do once"
--------------------------------------------------------------------------