I use phagemid pCDisplay3 and M13KO7 to construct Human Naive phage library. before digested with SfiI , I prepared ScFv (750bp) using gel purification. After electronic shock , ,plating on 2×YT（with 100ug/ml Ampicilin, 1% glucose）and cultivating in 37℃ overnight，I performed a PCR to verify the transformation efficiency. It was diappointing that only 70% of clone is positve(750bp), over 30% was negative(500bp or small). I sequenced the small fragment clone and the result indicate that there is only Vh or VL, why was there still so many half-ScFv( Vh or VL) being transformed into TG1 after SfiI digestion and gel pufication? (I am

definitely sure that I cut the only 750bp band after electrophoresis. )