A NLS-lacZ-polyA cassette was inserted into intron 19. It was flanked on the 5'end with a single FRT site and on the 3' end with a single loxP site. An additional loxP site followed by another FRT site was inserted into intron 23. Flp-mediated recombination in ES cells deleted the expression cassette and exons 20-23 (i.e. the kinase domain encoding exons). Western blot confirmed that no detectable protein is expressed from this allele. (J:226955)