Adenovirus-- Optimum conditions for ProteinaseK req.

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I am trying to use Proteinase K  for doing Adenovirus minipreps. I have previously used 
500mcg/ml of Prot-K, with 1% SDS and 20mM EDTA, but it does not seem to work at the moment.
I have also tried the concs. recommended in Maniatis, i.e. 0.5% SDS and 5mM EDTA, but this 
does not work efficiently either. Has anyone got a way around this, so I can get enough 
viral DNA back. Thanks