A loxP site and FRT-flanked neo cassette were inserted in intron 13 and a loxP site was inserted in intron 17 via homologous recombination. Cre-mediated recombination removed the neo cassette and exons 14-17. RT-PCR confirmed the expression of a truncated transcript lacking the CKK domain essential for the binding to microtubules. In polarized epithelial cells the mutant protien fails to collect in the apical cortical area of cell-cell junctions.