ABSTRACT
Analyzing the function of genes is the most promising approach to unravel the genetic program of development. This, however, is only possible when such genes are defined at both the genetic and at the molecular level. Insertional mutagenesis is a powerful way to increase the number of known genes. An alternative approach to investigate the mutagenic effect of integrated DNA is gene trapping. This technique has several important differences to the DNA injection methods. The neo stop codon is followed by an internal ribosome entry site, a start codon and the lacZ gene. The advantage of this construct is that every ES cell clone which is growing after neo selection should express the lacZ reporter from this dicistronic mRNA. As a consequence cloning of the transgene integration site was sometimes very complicated, since the construct was designed for the expression of the transgene and not for recloning.
