TOPO ligation - (Jun/22/2002 )

Hi
I met a trouble in TOPO ligation.  I tried to insert a 4.0 kb PCR product (using Pfu) into TOPO vector.  I got many both of white colonies and blue colonies.  After exation plasmid DNA from 12 white coloies, there were no insert!
Why? I cut off PCR product from modified TAE gel (low EDTA), and purifed using ULTRA-DA KIT. Please tell me why and how?

Yutong,
Many of these heat labile polymerases do not place an overhanging A at the end of the PCR product. Are you using TA TOPO or blunt TOPO if TA the cloning may not work with a Pfu generated amp product. Inubate the purified PCR product with 2.5 units of Taq. This will create an A overhang and your cloning results should improve.