radiolabelled supercoiled plasmid

[Gail Otulakowski]

I wish to label plasmid with 32P, but I can't use nick translation or 
random priming as these will affect the conformation and I need to look 
at supercoiled plasmid.  I think I will have to add radiolabelled 
inorganic phosphate to bacteria grown in minimal media - so two questions 
- has anyone grown E coli in M9 minimal for plasmid preps and will it 
make my yield lousy?  Also, M9 is normally buffered with phosphate - I 
can buffer with Tris instead but what are E.coli's minimal requirements 
for phosphate so I know how much hot stuff to add?