Tell me how to prepare the 25kb plasmid DNA

   Hello, 
   My name is Dongkook Park, graduate student of Seoul National
Student and I'm studying the molecular genetics of Drosphila
melanogaster.
   BTW, I have the obstacle to prepare the transposon plasmid for
transformation.
  I have subcloned 15kb DNA fragment at the pCaSpeR vector.
  So, I confirmed the clone through  mini prep.
 But, I does not  prepare the more amount of it by medium prep.

  Please, mail me how to prepare the large size DNA prep 
  whoever knows the tip.
  
  My address is followed;
     dkpark at power4.snu.ac.kr