blue/white screening - problem with recombinant colonies (Sep/06/2005 )

Hello everybody,
I am working on TA cloning and I use Fermentas InsTA cloning kit. I did blue/white screening and chose white colonies that are expected to have the insert, I screened almost 20 white colonies but when I did the colony PCR I can not see my insert, instead there is smaller fragment (my insert was 1000bp, but the fragment is ~500bp).What goes wrong

I think the smaller product (500bp) is much easier to insert into vertor than big product (1000bp) from my experience. You can try to clean the PCR product by cutting the right size of product if you clone from the PCR product.

Good luck.