Southwesterns

[Helen]

We perform Southwesterns on rat intestinal nuclear extracts and get a band at about 30 kDa 
(which we believe to be the correct size for the DNA-binding protein we are working with), but 
also  a very intense band showing up on the autorad at a molecular size  of about 15 kDa.  
Could this band be due to non-specific binding of our  P32-labeled oligo to Histones? I have 
seen similar bands in some articles, but this is not always the case.   Is there any way to get rid 
of this band? Are there any good references for Southwesterns that you can recommend?
Thanks,
Helen