cloning problem with pGADT7 (yeast 2Hybrid)

[george kapolas]

Hi all, 
  I' m trying to clone an insert of 1.7Kb to pGADT7 using NdeI and BamHI sites.. 
  After transformation in E. coli (DH5α) I get many colonies in 1/3 ratio vector/ insert ligation  and few colonies in my negative control . Although colony pcr gives me possitive results for 3 out of 4 colonies, when i do miniprep to the selected colonies, vectors  look empty. I am almost sure that i do not have problem with my pcr controls.
  any ideas ? 
  thanks, 
  george

       
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