What is: the toxic fragment in pBR322?

[Stephan Geley]

I have often heard that I would have to remove the "toxic fragment" from 
pBR322 plasmids if I intended to use a pBR322 derived plasmid in the 
context of eukaryotic expression. What exactly is the "toxic fragment" 
and what is its function?

Thanks,

Stephan Geley