Combinatorial strategy to build 8 residual vDNA clones. Each 5′-half clones (i.e., clone 1 and 6 shown on the left) were combined with four different 3′-half clones on the right through the overlapping EcoN1 sites (↓). An additional EcoN1 site (׀) present in all 3′-half clones, except clone 1 (see right), was abolished by site-directed mutagenesis prior to the combination. (PPT 55 kb)