Uncut lambda DNA showing bands??

[Knepper, Marc A]

Dear Netters:                                                                   
                                                                                
Here's a puzzle for you: I purified some lambda DNA + insert using a            
QIAGEN column, then ran 1 ug on a gel. Instead of seeing one intense            
band near the top, there were four distinct bands! I loaded some more of        
the DNA on the gel in another slot just to make sure this is what I was         
seeing. Then I did a digest with three different enzymes. All of the            
expected bands for each enzyme showed up on the gel, and it appears that        
the bands I'm seeing in the uncut DNA do not interfere with digestion.          
                                                                                
Has anybody else ever seen anything like this? Contamination with               
restriction enzymes could be ruled out since the DNA was placed at -4C          
immediately after purification, was taken out to use on the gel and             
returned immediately to the freezer. Any comments or ideas as to what           
this might be? Is it possible that it could be the left and right arms +        
insert showing up, or supercoiling? This has really baffled me? I would         
appreciate any help you can give. Thank you in advance.                         
                                                                                
Marc Knepper                                                                    
mknepper at nmu.edu                                                                
                                                                               
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