Adenoviral DNA minipreps

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I have been trying to do Adenovirus DNA minipreps on some recombinant 
adenoviruses. I use recomb. ad5 infected 293 cells lysate, freeze-thawed in 
Tris-saline. I have previously used 500ug/ml of Proteinase K in 1% SDS and
20mM EDTA. But now the same conditions are not giving results. I get very
little or no DNA at all. The DNA that I get then does not cut with HindIII.

I have tried altering conc. of SDS to 0.5% and EDTA to 5mM but not signi-
ficant change is observed. 

Can anyone please inform me of any tested protocol for the DNA minipreps
for Adenovirus.
Thanks, Obaid