Shearing/cleaving DNA for shuffling

[Louis Hom]

I've noticed that people generally cleave their DNA for shuffling 
enzymatically (e.g., DNase I) instead of mechanically (e.g., sonication).  
What are the reasons for this?  Are sonication products too small or too 
heterogenous?  Is it because you lose specificity for products with 5' 
phosphates?
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______________________________________________________________________________
Lou Hom >K'93			     
lhom at ocf.berkeley.edu		
http://www.ocf.berkeley.edu/~lhom/