Figure 1. Basis of the recombination in pSpliceExpress. (a) The lambda integration system. Integrase action leads to a recombination between the attP and attB sites located in the lambda and E. coli genomes, respectively. The attP and attB sites recombine to attL and attR sites flanking the integrated lambda DNA; (b) Adaptation of the integration system for pSpliceExpress. pSpliceExpress contains the ccdB gene and a CmR resistance used for selection that is flanked by attP sites. Upon recombination with a PCR fragment containing attB sites, this marker is lost and colonies with the inserted PCR product grow in the appropriate E. coli strain.

Figure 2. Example of the analysis. (a) Ethidium bromide‐stained gel showing minipreps of colonies after recombination. The DNA was analyzed by KpnI digestion. All colonies have inserts, but colonies 1 and 4 represent aberrant recombinations that resulted in wrong vector or insert sizes; (b) Example of cotransfection of the resulting minigene with an increasing amount of the splicing factor Tra2‐beta1, which represses inclusion of the alternative exon.