Recombination-mediated cassette exchange (RMCE) was used to replace exons 76 through 89 with an frt-flanked cassette containing a cDNA for exons 76 through 89 and a floxed neo gene. The cDNA contains mutations in exon 88 that result in amino acid substitutions of RHRR with AATA and disrupt the NPXY1 site. (J:144146)